4-[2-(2-fluorophenoxymethyl)phenyl]piperidine compounds

ABSTRACT

The invention relates to compounds of formula I: 
                         
where a, R 1 , and R 3-6  are as defined in the specification, or a pharmaceutically acceptable salt thereof. The compounds of formula I are serotonin and norepinephrine reuptake inhibitors. The invention also relates to pharmaceutical compositions comprising such compounds; methods of using such compounds; and process and intermediates for preparing such compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/114,541, filed on Nov. 14, 2008; the entire disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to 4-[2-(2-fluorophenoxymethyl)phenyl]piperidine compounds having activity as serotonin (5-HT) and norepinephrine (NE) reuptake inhibitors. The invention also relates to pharmaceutical compositions comprising such compounds, processes and intermediates for preparing such compounds and methods of using such compounds to treat a pain disorder, such as neuropathic pain, and other ailments.

2. State of the Art

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage (International Association for the Study of Pain (IASP), Pain Terminology). Chronic pain persists beyond acute pain or beyond the expected time for an injury to heal (American Pain Society. “Pain Control in the Primary Care Setting.” 2006:15). Neuropathic pain is pain initiated or caused by a primary lesion or dysfunction in the nervous system. Peripheral neuropathic pain occurs when the lesion or dysfunction affects the peripheral nervous system and central neuropathic pain when the lesion or dysfunction affects the central nervous system (IASP).

Several types of therapeutic agents are currently used to treat neuropathic pain including, for example, tricyclic antidepressants (TCAs), serotonin and norepinephrine reuptake inhibitors (SNRIs), calcium channel ligands (e.g., gabapentin and pregabalin), topical lidocaine, and opioid agonists (e.g., morphine, oxycodone, methadone, levorphanol and tramadol). However, neuropathic pain can be very difficult to treat with no more than 40-60% of patients achieving, at best, partial relief of their pain (Dworkin et al. (2007) Pain 132:237-251). Moreover, all of the therapeutic agents currently used to treat neuropathic pain have various side effects (e.g., nausea, sedation, dizziness and somnolence) that can limit their effectiveness in some patients (Dworkin et al. supra).

SNRIs, such as duloxetine and venlafaxine, are often used as first line therapy for treating neuropathic pain. These agents inhibit the reuptake of both serotonin (5-hydroxytrypamine, 5-HT) and norepinephrine (NE) by binding to the serotonin and norepinephrine transporters (SERT and NET, respectively). However, both duloxetine and venlafaxine have higher affinity for SERT relative to NET (Vaishnavi et al. (2004) Biol. Psychiatry 55(3):320-322).

Preclinical studies suggest that inhibition of both SERT and NET may be necessary for maximally effective treatment of neuropathic and other chronic pain states (Jones et al. (2006) Neuropharmacology 51(7-8):1172-1180; Vickers et al. (2008) Bioorg. Med. Chem. Lett. 18:3230-3235; Fishbain et al. (2000) Pain Med. 1(4):310-316; and Mochizucki (2004) Human Psychopharmacology 19:S15-S19). However, in clinical studies, the inhibition of SERT has been reported to be related to nausea and other side effects (Greist et al. (2004) Clin. Ther. 26(9):1446-1455). Thus, therapeutic agents having more balanced SERT and NET affinity or slightly higher NET affinity are expected to be particularly useful for treating chronic pain while producing fewer side effects, such as nausea.

Thus, a need exists for novel compounds that are useful for treating chronic pain, such as neuropathic pain. In particular, a need exists for novel compounds that are useful for treating chronic pain and that have reduced side effects, such as nausea. A need also exists for novel dual-acting compounds that inhibit both SERT and NET with high affinity (e.g., pK_(i)≧8.0 or K_(i)≦10 nM) and balanced inhibition (e.g., a SERT/NET binding K_(i) ratio of 0.1 to 100).

SUMMARY OF THE INVENTION

The present invention provides novel compounds that have been found to possess serotonin reuptake inhibitory activity and norepinephrine reuptake inhibitory activity. Accordingly, compounds of the invention are expected to be useful and advantageous as therapeutic agents for those diseases and disorders that can be treated by inhibition of the serotonin and/or norepinephrine transporter, such as neuropathic pain.

One aspect of the invention relates to compounds of formula I:

where: a is 0, 1, 2, 3, or 4; each R¹ is independently halo or trifluoromethyl; R³ is hydrogen, halo, or —C₁₋₆alkyl; R⁴, R⁵, and R⁶ are independently hydrogen or halo; or a pharmaceutically acceptable salt thereof.

Another aspect of the invention relates to compounds of formula II:

where:

(a) R³ and R⁵ are hydrogen and:

-   -   (i) R⁴ is fluoro, R⁶ is fluoro, and a is 0;     -   (ii) R⁴ is fluoro, R⁶ is fluoro, a is 1, and R¹ is 4-fluoro,         5-fluoro, 5-trifluoromethyl, or 6-fluoro;     -   (iii) R⁴ is fluoro, R⁶ is fluoro, a is 2, and R¹ is         4,5-difluoro, 4,6-difluoro, or 5,6-difluoro;     -   (iv) R⁴ is fluoro, R⁶ is chloro, and a is 0;     -   (v) R⁴ is chloro, R⁶ is fluoro, and a is 0; or     -   (vi) R⁴ is bromo, R⁶ is chloro, and a is 0; or

(b) R³ and R⁴ are hydrogen, R⁵ is fluoro, R⁶ is chloro, and:

-   -   (i) a is 0;     -   (ii) a is 1 and R¹ is 5-fluoro or 6-fluoro; or     -   (iii) a is 2 and R¹ is 4,6-difluoro; or

(c) R⁴ and R⁵ are hydrogen, R⁶ is fluoro and;

-   -   (i) R³ is fluoro and a is 0;     -   (ii) R³ is fluoro, a is 1, and R¹ is 3-fluoro, 5-fluoro,         5-trifluoromethyl, or 6-fluoro;     -   (iii) R³ is fluoro, a is 2, and R¹ is 4,6-difluoro; or     -   (iv) R³ is chloro or methyl, and a is 0; or

(d) R³, R⁴, and R⁵ are hydrogen and:

-   -   (i) R⁶ is H, and a is 0;     -   (ii) R⁶ is H, a is 1, and R¹ is 5-fluoro or 6-fluoro;     -   (iii) R⁶ is fluoro and a is 0;     -   (iv) R⁶ is fluoro, a is 1, and R¹ is 4-fluoro, 5-fluoro, or         6-fluoro;     -   (v) R⁶ is fluoro, a is 2, and R¹ is 4,5-difluoro or         4,6-difluoro;     -   (vi) R⁶ is chloro and a is 0;     -   (vii) R⁶ is chloro, a is 1, and R¹ is 4-fluoro, 6-fluoro, or         5-trifluoromethyl;     -   (viii) R⁶ is chloro, a is 2, and R¹ is 4,5-difluoro; or     -   (ix) R⁶ is bromo and a is 0;

or a pharmaceutically acceptable salt thereof.

Yet another aspect of the invention relates to pharmaceutical compositions comprising a pharmaceutically acceptable carrier and a compound of the invention. Such compositions may optionally contain other active agents such as anti-Alzheimer's agents, anticonvulsants, antidepressants, anti-Parkinson's agents, dual serotonin-norepinephrine reuptake inhibitors, non-steroidal anti-inflammatory agents, norepinephrine reuptake inhibitors, opioid agonists, opioid antagonists, selective serotonin reuptake inhibitors, sodium channel blockers, sympatholytics, and combinations thereof. Accordingly, in yet another aspect of the invention, a pharmaceutical composition comprises a compound of the invention, a second active agent, and a pharmaceutically acceptable carrier. Another aspect of the invention relates to a combination of active agents, comprising a compound of the invention and a second active agent. The compounds of the invention can be formulated together or separately from the additional agent(s). When formulated separately, a pharmaceutically acceptable carrier may be included with the additional agent(s). Thus, yet another aspect of the invention relates to a combination of pharmaceutical compositions, the combination comprising: a first pharmaceutical composition comprising a compound of formula I or a pharmaceutically acceptable salt thereof and a first pharmaceutically acceptable carrier; and a second pharmaceutical composition comprising a second active agent and a second pharmaceutically acceptable carrier. The invention also relates to a kit containing such pharmaceutical compositions, for example where the first and second pharmaceutical compositions are separate pharmaceutical compositions.

Compounds of the invention possess serotonin reuptake inhibitory activity and norepinephrine reuptake inhibitory activity, and are therefore expected to be useful as therapeutic agents for treating patients suffering from a disease or disorder that is treated by the inhibition of the serotonin and/or the norepinephrine transporter. Thus, one aspect of the invention relates to a method of treating: a pain disorder such as neuropathic pain or fibromyalgia; a depressive disorder such as major depression; an affective disorder such as an anxiety disorder; attention deficit hyperactivity disorder; a cognitive disorder such as dementia; stress urinary incontinence; chronic fatigue syndrome; obesity; or vasomotor symptoms associated with menopause, comprising administering to a patient a therapeutically effective amount of a compound of the invention.

Still another aspect of the invention relates to a method for inhibiting serotonin reuptake in a mammal comprising administering to the mammal, a serotonin transporter-inhibiting amount of a compound of the invention. Yet another aspect of the invention relates to a method for inhibiting norepinephrine reuptake in a mammal comprising administering to the mammal, a norepinephrine transporter-inhibiting amount of a compound of the invention. And another aspect of the invention is directed to a method for inhibiting serotonin reuptake and norepinephrine reuptake in a mammal comprising administering to the mammal, a serotonin transporter- and norepinephrine transporter-inhibiting amount of a compound of the invention.

Among the compounds of formula I, compounds of particular interest are those having an inhibitory constant (pK_(i)) at SERT greater than or equal to about 7.9 and an inhibitory constant (pK_(i)) at NET greater than or equal to about 8.0. In another embodiment, compounds of interest have balanced SERT and NET activity, i.e., have the same pK_(i) value at both SERT and NET±0.5. Further compounds of particular interest are those having a serotonin reuptake inhibition pIC₅₀ values of greater than or equal to about 7.0 and a norepinephrine reuptake inhibition pIC₅₀ values of greater than or equal to about 7.0.

Since compounds of the invention possess serotonin reuptake inhibitory activity and norepinephrine reuptake inhibitory activity, such compounds are also useful as research tools. Accordingly, one aspect of the invention relates to methods of using the compounds of the invention as research tools, comprising conducting a biological assay using a compound of the invention. Compounds of the invention can also be used to evaluate new chemical compounds. Thus another aspect of the invention relates to a method of evaluating a test compound in a biological assay, comprising: (a) conducting a biological assay with a test compound to provide a first assay value; (b) conducting the biological assay with a compound of the invention to provide a second assay value; wherein step (a) is conducted either before, after or concurrently with step (b); and (c) comparing the first assay value from step (a) with the second assay value from step (b). Exemplary biological assays include a serotonin reuptake assay and a norepinephrine reuptake assay. Still another aspect of the invention relates to a method of studying a biological system or sample comprising serotonin transporters, norepinephrine transporters, or both, the method comprising: (a) contacting the biological system or sample with a compound of the invention; and (b) determining the effects caused by the compound on the biological system or sample.

The invention also relates to processes and intermediates useful for preparing compounds of the invention. Accordingly, one aspect of the invention relates to a process for preparing compounds of formula I, the process comprising deprotecting a compound of formula III:

or a salt thereof, where P is an amino-protecting group to provide compounds of formula I or II, where a, R′, and R³⁻⁶ are as defined for formulas I or II, respectively. In other aspects, the invention relates to novel intermediates used in such processes.

Yet another aspect of the invention relates to the use of compounds of the invention for the manufacture of medicaments, especially for the manufacture of medicaments useful for treating pain disorders, depressive disorders, affective disorders, attention deficit hyperactivity disorder, cognitive disorders, stress urinary incontinence, for inhibiting serotonin reuptake in a mammal, or for inhibiting norepinephrine reuptake in a mammal. Still another aspect of the invention relates to the use of compounds of the invention as research tools. Other aspects and embodiments of the invention are disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION Definitions

When describing the compounds, compositions, methods and processes of the invention, the following terms have the following meanings unless otherwise indicated. Additionally, as used herein, the singular forms “a,” “an” and “the” include the corresponding plural forms unless the context of use clearly dictates otherwise. The terms “comprising”, “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. All numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used herein are to be understood as being modified in all instances by the term “about,” unless otherwise indicated. Accordingly, the numbers set forth herein are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each number should at least be construed in light of the reported significant digits and by applying ordinary rounding techniques. The term “alkyl” means a monovalent saturated hydrocarbon group which may be linear or branched. Unless otherwise defined, such alkyl groups typically contain from 1 to 10 carbon atoms and include, for example, —C₁₋₂alkyl, —C₁₋₃alkyl, —C₁₋₄alkyl, —C₁₋₆alkyl, and —C₁₋₈alkyl. Representative alkyl groups include, by way of example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tent-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, and the like.

When a specific number of carbon atoms is intended for a particular term used herein, the number of carbon atoms is shown preceding the term as subscript. For example, the term “—C₁₋₆alkyl” means an alkyl group having from 1 to 6 carbon atoms, and the term “—C₁₋₄alkylene” means an alkylene group having from 1 to 4 carbon atoms, where the carbon atoms are in any acceptable configuration.

The term “alkylene” means a divalent saturated hydrocarbon group that may be linear or branched. Unless otherwise defined, such alkylene groups typically contain from 0 to 10 carbon atoms and include, for example, —C₀₋₁alkylene, —C₀₋₂alkylene, —C₀₋₃alkylene, —C₀₋₆alkylene, —C₁₋₄alkylene, —C₂₋₄alkylene and —C₁₋₆alkylene. Representative alkylene groups include, by way of example, methylene, ethane-1,2-diyl (“ethylene”), propane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, and the like. It is understood that when the alkylene term includes zero carbons such as —C₀₋₁alkylene-, —C₀₋₃alkylene- or —C₀₋₆alkylene-, such terms are intended to include the absence of carbon atoms, i.e., the alkylene group is not present except for a covalent bond attaching the groups separated by the alkylene term.

The term “alkynyl” means a monovalent unsaturated hydrocarbon group which may be linear or branched and which has at least one, and typically 1, 2 or 3, carbon-carbon triple bonds. Unless otherwise defined, such alkynyl groups typically contain from 2 to 10 carbon atoms and include, for example, —C₂₋₄alkynyl, —C₂₋₆alkynyl and —C₃₋₁₀alkynyl. Representative alkynyl groups include, by way of example, ethynyl, n-propynyl, n-but-2-ynyl, n-hex-3-ynyl, and the like.

The term “halo” means fluoro, chloro, bromo and iodo.

As used herein, the phrase “of the formula”, “having the formula” or “having the structure” is not intended to be limiting and is used in the same way that the term “comprising” is commonly used.

The term “pharmaceutically acceptable” refers to a material that is not biologically or otherwise unacceptable when used in the invention. For example, the term “pharmaceutically acceptable carrier” refers to a material that can be incorporated into a composition and administered to a patient without causing unacceptable biological effects or interacting in an unacceptable manner with other components of the composition. Such pharmaceutically acceptable materials typically have met the required standards of toxicological and manufacturing testing, and include those materials identified as suitable inactive ingredients by the U.S. Food and Drug Administration.

The term “pharmaceutically acceptable salt” means a salt prepared from a base or an acid which is acceptable for administration to a patient, such as a mammal (e.g., salts having acceptable mammalian safety for a given dosage regime). However, it is understood that the salts covered by the invention are not required to be pharmaceutically acceptable salts, such as salts of intermediate compounds that are not intended for administration to a patient. Pharmaceutically acceptable salts can be derived from pharmaceutically acceptable inorganic or organic bases and from pharmaceutically acceptable inorganic or organic acids. In addition, when a compound of formula I contains both a basic moiety, such as an amine, and an acidic moiety such as a carboxylic acid, zwitterions may be formed and are included within the term “salt” as used herein. Salts derived from pharmaceutically acceptable inorganic bases include ammonium, calcium, copper, ferric, ferrous, lithium, magnesium, manganic, manganous, potassium, sodium, and zinc salts, and the like. Salts derived from pharmaceutically acceptable organic bases include salts of primary, secondary and tertiary amines, including substituted amines, cyclic amines, naturally-occurring amines, and the like, such as arginine, betaine, caffeine, choline, N,N′-dibenzylethylenediamine, diethylamine, 2-diethylaminoethanol, 2-dimethylaminoethanol, ethanolamine, ethylenediamine, N-ethylmorpholine, N-ethylpiperidine, glucamine, glucosamine, histidine, hydrabamine, isopropylamine, lysine, methylglucamine, morpholine, piperazine, piperadine, polyamine resins, procaine, purines, theobromine, triethylamine, trimethylamine, tripropylamine, tromethamine, and the like. Salts derived from pharmaceutically acceptable inorganic acids include salts of boric, carbonic, hydrohalic (hydrobromic, hydrochloric, hydrofluoric or hydroiodic), nitric, phosphoric, sulfamic and sulfuric acids. Salts derived from pharmaceutically acceptable organic acids include salts of aliphatic hydroxyl acids (e.g., citric, gluconic, glycolic, lactic, lactobionic, malic, and tartaric acids), aliphatic monocarboxylic acids (e.g., acetic, butyric, formic, propionic and trifluoroacetic acids), amino acids (e.g., aspartic and glutamic acids), aromatic carboxylic acids (e.g., benzoic, p-chlorobenzoic, diphenylacetic, gentisic, hippuric, and triphenylacetic acids), aromatic hydroxyl acids (e.g., o-hydroxybenzoic, p-hydroxybenzoic, 1-hydroxynaphthalene-2-carboxylic and 3-hydroxynaphthalene-2-carboxylic acids), ascorbic, dicarboxylic acids (e.g., fumaric, maleic, oxalic and succinic acids), glucuronic, mandelic, mucic, nicotinic, orotic, pamoic, pantothenic, sulfonic acids (e.g., benzenesulfonic, camphorsulfonic, edisylic, ethanesulfonic, isethionic, methanesulfonic, naphthalenesulfonic, naphthalene-1,5-disulfonic, naphthalene-2,6-disulfonic and p-toluenesulfonic acids), xinafoic acid, and the like.

The term “solvate” means a complex or aggregate formed by one or more molecules of a solute, e.g., a compound of formula I or a pharmaceutically acceptable salt thereof, and one or more molecules of a solvent. Such solvates are typically crystalline solids having a substantially fixed molar ratio of solute and solvent. Representative solvents include, by way of example, water, methanol, ethanol, isopropanol, acetic acid, and the like. When the solvent is water, the solvate formed is a hydrate.

The term “therapeutically effective amount” means an amount sufficient to effect treatment when administered to a patient in need thereof, i.e., the amount of drug needed to obtain the desired therapeutic effect. For example, a therapeutically effective amount for treating neuropathic pain is an amount of compound needed to, for example, reduce, suppress, eliminate or prevent the symptoms of neuropathic pain or to treat the underlying cause of neuropathic pain. On the other hand, the term “effective amount” means an amount sufficient to obtain a desired result, which may not necessary be a therapeutic result. For example, when studying a system comprising a norepinephrine transporter, an “effective amount” may be the amount needed to inhibit norepinephrine reuptake.

The term “treating” or “treatment” as used herein means the treating or treatment of a disease or medical condition (such as neuropathic pain) in a patient, such as a mammal (particularly a human), that includes one or more of the following: (a) preventing the disease or medical condition from occurring, i.e., prophylactic treatment of a patient; (b) ameliorating the disease or medical condition, i.e., eliminating or causing regression of the disease or medical condition in a patient; (c) suppressing the disease or medical condition, i.e., slowing or arresting the development of the disease or medical condition in a patient; or (d) alleviating the symptoms of the disease or medical condition in a patient. For example, the term “treating neuropathic pain” would include preventing neuropathic pain from occurring, ameliorating neuropathic pain, suppressing neuropathic pain, and alleviating the symptoms of neuropathic pain. The term “patient” is intended to include those mammals, such as humans, that are in need of treatment or disease prevention, that are presently being treated for disease prevention or treatment of a specific disease or medical condition, as well as test subjects in which compounds of the invention are being evaluated or being used in a assay, for example an animal model.

All other terms used herein are intended to have their ordinary meaning as understood by those of ordinary skill in the art to which they pertain.

In one aspect, this invention relates to compounds of formula I:

or a pharmaceutically acceptable salt thereof.

As used herein, the term “compound of the invention” or “compounds of the invention” include all compounds encompassed by formulas I, II and III, such as the species embodied in formulas IIa, IIb, IIc, and IId, and all other subspecies of such formulas. In addition, when a compound of the invention contain a basic or acidic group (e.g., amino or carboxyl groups), the compound can exist as a free base, free acid, a zwitterion, or in various salt forms. All such salt forms are included within the scope of the invention. Accordingly, those skilled in the art will recognize that reference to compounds herein, for example, reference to a “compound of the invention” or a “compound of formula I” includes a compound of formula I as well as pharmaceutically acceptable salts of that compound unless otherwise indicated. Furthermore, solvates are also included within the scope of this invention.

Compounds of the invention, as well as those compounds used in their synthesis, may also include isotopically-labeled compounds, i.e., where one or more atoms have been enriched with atoms having an atomic mass different from the atomic mass predominately found in nature. Examples of isotopes that may be incorporated into the compounds of the ²H, ³H, ¹³C, ¹⁴C, ¹⁵N, ¹⁸O, ¹⁷O, ³⁵S, invention, for example, include, but are not limited to, ³⁶Cl, and ¹⁸F. Of particular interest are compounds of formula I enriched in tritium or carbon-14 which can be used, for example, in tissue distribution studies; compounds of formula I enriched in deuterium especially at a site of metabolism resulting, for example, in compounds having greater metabolic stability; and compounds of formula I enriched in a positron emitting isotope, such as ¹¹C, ¹⁸F, ¹⁵O and ¹³N, which can be used, for example, in Positron Emission Topography (PET) studies.

The compounds of the invention have been found to possess serotonin reuptake inhibitory activity and norepinephrine reuptake inhibitory activity. Among other properties, such compounds are expected to be useful as therapeutic agents for treating chronic pain, such as neuropathic pain. By combining dual activity into a single compound, double therapy can be achieved, i.e., serotonin reuptake inhibitory activity and norepinephrine reuptake inhibitory activity, using a single active component. Since pharmaceutical compositions containing one active component are typically easier to formulate than compositions containing two active components, such single-component compositions provide a significant advantage over compositions containing two active components.

Many combined serotonin and norepinephrine reuptake inhibitors (SNRIs) are more selective for SERT than for NET. For example, milnacipran, duloxetine, and venlafaxine exhibit 2.5-fold, 10-fold, and 100-fold selectivity (measured as pK_(i)) for SERT over NET, respectively. Some, however, are less selective, such as bicifadine, which has a pK_(i) at SERT of 7.0 and a pK_(i) at NET of 6.7. Since it may be desirable to avoid selective compounds, in one embodiment of the invention the compounds have a more balanced SERT and NET activity, i.e., have the same pK_(i) value at both SERT and NET±0.5.

The compounds described herein have typically been named using the AutoNom feature of the commercially-available MDL® ISIS/Draw software (Symyx, Santa Clara, Calif.). Typically, compounds of the invention have been named as 4-[2-(2-fluorophenoxymethyl)phenyl]piperidines. Partial numbering of the compounds described herein is as follows:

Representative Embodiments

The following substituents and values are intended to provide representative examples of various aspects and embodiments of the invention. These representative values are intended to further define and illustrate such aspects and embodiments and are not intended to exclude other embodiments or to limit the scope of the invention. In this regard, the representation that a particular value or substituent is preferred is not intended in any way to exclude other values or substituents from the invention unless specifically indicated.

In one aspect, this invention relates to compounds of formula I:

In compounds of formula I, The integer a can be 0, 1, 2, 3, or 4. Each R¹ is independently halo or trifluoromethyl. R³ is hydrogen, halo, or —C₁₋₆alkyl. R⁴, R⁵, and R⁶ are independently hydrogen or halo. Exemplary halo groups include fluoro, chloro, bromo, and iodo. Exemplary —C₁₋₆alkyl groups include —CH₃, —CH₂CH₃, and —CH(CH₃)₂. In one embodiment, R³ is hydrogen, fluoro, chloro, or methyl. In one embodiment, R⁴ is hydrogen, fluoro, chloro, or bromo. In one embodiment, R⁵ is hydrogen or fluoro. In one embodiment, R⁶ is hydrogen, fluoro, chloro, or bromo.

In one embodiment of compounds of formula I, a is 0. This can be depicted as formula Ia:

In one embodiment of compounds of formula Ia, R³ is hydrogen, fluoro, chloro, or methyl; R⁴ is hydrogen, fluoro, chloro, or bromo; R⁵ is hydrogen or fluoro; and R⁶ is hydrogen, fluoro, chloro, or bromo.

In another embodiment of compounds of formula I, a is 1. This can be depicted as formula Ib:

In one embodiment of compounds of formula Ib, R¹ is 3-fluoro, 4-fluoro, 5-fluoro, 5-trifluoromethyl, or 6-fluoro. In another embodiment, of compounds of formula Ib, R³ is hydrogen or fluoro; R⁴ is hydrogen or fluoro; R⁵ is hydrogen or fluoro; and R⁶ is hydrogen, fluoro or chloro.

In yet another embodiment of compounds of formula I, a is 2. This can be depicted as formula Ic:

In one embodiment of compounds of formula Ic, R¹ is 4,5-difluoro, 4,6-difluoro, or 5,6-difluoro. In another embodiment, of compounds of formula Ib, R³ is hydrogen or fluoro; R⁴ is hydrogen or fluoro; R⁵ is hydrogen or fluoro; and R⁶ is hydrogen, fluoro or chloro.

In one particular aspect of the invention, the compounds of formula I exhibit a SERT pK_(i)≧7.9 and a NET pK_(i)≧8.

In another aspect, this invention relates to compounds of formula II:

where:

(a) R³ and R⁵ are hydrogen and:

-   -   (i) R⁴ is fluoro, R⁶ is fluoro, and a is 0;     -   (ii) R⁴ is fluoro, R⁶ is fluoro, a is 1, and R¹ is 4-fluoro,         5-fluoro, 5-trifluoromethyl, or 6-fluoro;     -   (iii) R⁴ is fluoro, R⁶ is fluoro, a is 2, and R¹ is         4,5-difluoro, 4,6-difluoro, or 5,6-difluoro;     -   (iv) R⁴ is fluoro, R⁶ is chloro, and a is 0;     -   (v) R⁴ is chloro, R⁶ is fluoro, and a is 0; or     -   (vi) R⁴ is bromo, R⁶ is chloro, and a is 0; or

(b) R³ and R⁴ are hydrogen, R⁵ is fluoro, R⁶ is chloro, and:

-   -   (i) a is 0;     -   (ii) a is 1 and R¹ is 5-fluoro or 6-fluoro; or     -   (iii) a is 2 and R¹ is 4,6-difluoro; or

(c) R⁴ and R⁵ are hydrogen, R⁶ is fluoro and;

-   -   (i) R³ is fluoro and a is 0;     -   (ii) R³ is fluoro, a is 1, and R¹ is 3-fluoro, 5-fluoro,         5-trifluoromethyl, or 6-fluoro;     -   (iii) R³ is fluoro, a is 2, and R¹ is 4,6-difluoro; or     -   (iv) R³ is chloro or methyl, and a is 0; or

(d) R³, R⁴, and R⁵ are hydrogen and:

-   -   (i) R⁶ is H and a is 0;     -   (ii) R⁶ is H, a is 1, and R¹ is 5-fluoro or 6-fluoro;     -   (iii) R⁶ is fluoro and a is 0;     -   (iv) R⁶ is fluoro, a is 1, and R¹ is 4-fluoro, 5-fluoro, or         6-fluoro;     -   (v) R⁶ is fluoro, a is 2, and R¹ is 4,5-difluoro or         4,6-difluoro;     -   (vi) R⁶ is chloro and a is 0;     -   (vii) R⁶ is chloro, a is 1, and R¹ is 4-fluoro, 6-fluoro, or         5-trifluoromethyl;     -   (viii) R⁶ is chloro, a is 2, and R¹ is 4,5-difluoro; or     -   (ix) R⁶ is bromo and a is 0;

or a pharmaceutically acceptable salt thereof.

In one embodiment of compounds of formula II, R³ and R⁵ are hydrogen. This can be depicted as formula IIa:

In one embodiment of compounds of formula IIa, R⁴ is fluoro, R⁶ is fluoro, and a is 0. In another embodiment, R⁴ is fluoro, R⁶ is fluoro, a is 1 and R¹ is 4-fluoro, 5-fluoro, 5-trifluoromethyl, or 6-fluoro. In another embodiment, R⁴ is fluoro, R⁶ is fluoro, a is 2 and R¹ is 4,5-difluoro, 4,6-difluoro, or 5,6-difluoro. In one embodiment, R⁴ is fluoro, R⁶ is chloro, and a is 0. In another embodiment, R⁴ is chloro, R⁶ is fluoro, and a is 0. In another embodiment, R⁴ is bromo, R⁶ is chloro, and a is 0. In yet another embodiment, these compounds of formula IIa exhibit a SERT pK_(i)≧7.9 and a NET pK_(i)≧8.

In another embodiment of compounds of formula II, R³ and R⁴ are hydrogen, R⁵ is fluoro, and R⁶ is chloro. This can be depicted as formula IIb:

In one embodiment of compounds of formula IIb, a is 0. In another embodiment, a is 1 and R¹ is 5-fluoro or 6-fluoro. In another embodiment, a is 2 and R¹ is 4,6-difluoro. In yet another embodiment, these compounds of formula IIb exhibit a SERT pK_(i)≧7.9 and a NET pK_(i)≧8.

In still another embodiment of compounds of formula II, R⁴ and R⁵ are hydrogen and R⁶ is fluoro. This can be depicted as formula IIc:

In one embodiment of compounds of formula IIc, R³ is fluoro and a is 0. In another embodiment, R³ is fluoro, a is 1, and R¹ is 3-fluoro, 5-fluoro, 5-trifluoromethyl, or 6-fluoro. In another embodiment, R³ is fluoro, a is 2, and R¹ is 4,6-difluoro. In another embodiment, R³ is chloro or methyl, and a is 0. In yet another embodiment, these compounds of formula IIc exhibit a SERT pK_(i)≧7.9 and a NET pK_(i)≧8.

In yet another embodiment of compounds of formula II, R³, R⁴, and R⁵ are hydrogen. This can be depicted as formula IId:

In one embodiment of compounds of formula IId, R⁶ is H and a is 0. In another embodiment, R⁶ is H, a is 1, and R¹ is 5-fluoro or 6-fluoro. In another embodiment, R⁶ is fluoro or chloro, and a is 0. In yet another embodiment, R⁶ is fluoro, a is 1, and R¹ is 4-fluoro, 5-fluoro, or 6-fluoro. In yet another embodiment, R⁶ is or chloro, a is 1, and R¹ is 4-fluoro, 6-fluoro, or 5-trifluoromethyl. In one embodiment, R⁶ is fluoro, a is 2, and R¹ is 4,5-difluoro or 4,6-difluoro. In one embodiment, R⁶ is chloro, a is 2, and R¹ is 4,5-difluoro. In another embodiment, R⁶ is bromo and a is 0. In yet another embodiment, these compounds of formula IId exhibit a SERT pK_(i)≧7.9 and a NET pK_(i)≧8.

In one embodiment, the compounds of the invention have high affinity for NET and have a relatively balanced affinity for SERT relative to NET, and in one embodiment, higher affinity for NET relative to SERT. In one particular embodiment, the compounds of the invention exhibit a SERT pK_(i)≧7.9 and a NET pK_(i)≧8. Surprisingly, this balance of SERT and NET activity is not found in some structurally similar compounds. For example, the following compound of the invention:

exhibits a SERT pK_(i) of 7.9 and a NET pK_(i) of 8.3, as determined in Assay 1. Evaluated in the same assay, the following compounds exhibit either low binding at both targets (unsubstituted) or greater binding at SERT than at NET (2-chloro and 2-methyl):

Compound SERT pK_(i) NET pK_(i) unsubstituted 7.5 7.4 2-chloro 8.4 7.5 2-methyl 8.8 7.5

General Synthetic Procedures

Compounds of the invention can be prepared from readily available starting materials using the following general methods, the procedures set forth in the Examples, or by using other methods, reagents, and starting materials that are known to those skilled in the art. Although the following procedures may illustrate a particular embodiment of the invention, it is understood that other embodiments of the invention can be similarly prepared using the same or similar methods or by using other methods, reagents and starting materials known to those of ordinary skill in the art. It will also be appreciated that where typical or preferred process conditions (i.e., reaction temperatures, times, mole ratios of reactants, solvents, pressures, etc.) are given, other process conditions can also be used unless otherwise stated. While optimum reaction conditions will typically vary depending on various reaction parameters such as the particular reactants, solvents and quantities used, those of ordinary skill in the art can readily determine suitable reaction conditions using routine optimization procedures.

Additionally, as will be apparent to those skilled in the art, conventional protecting groups may be necessary or desired to prevent certain functional groups from undergoing undesired reactions. The choice of a suitable protecting group for a particular functional group as well as suitable conditions and reagents for protection and deprotection of such functional groups are well-known in the art. Protecting groups other than those illustrated in the procedures described herein may be used, if desired. For example, numerous protecting groups, and their introduction and removal, are described in T. W. Greene and G. M. Wuts, Protecting Groups in Organic Synthesis, Third Edition, Wiley, New York, 1999, and references cited therein.

More particularly, in the schemes below, P represents an “amino-protecting group,” a term used herein to mean a protecting group suitable for preventing undesired reactions at an amino group. Representative amino-protecting groups include, but are not limited to, t-butoxycarbonyl (Boc), trityl (Tr), benzyloxycarbonyl (Cbz), 9-fluorenylmethoxycarbonyl (Fmoc), formyl, benzyl, and the like. Standard deprotection techniques and reagents such as TFA in DCM or HCl in 1,4-dioxane, methanol, or ethanol, are used to remove protecting groups, when present. For example, a Boc group can be removed using an acidic reagent such as hydrochloric acid, trifluoroacetic acid, and the like; while a Cbz group can be removed by employing catalytic hydrogenation conditions such as H₂ (1 atm), 10% Pd/C in an alcoholic solvent. The schemes are illustrated with Boc as the protecting group.

In the schemes below, L represents a “leaving group,” a term used herein to mean a functional group or atom which can be displaced by another functional group or atom in a substitution reaction, such as a nucleophilic substitution reaction. By way of example, representative leaving groups include chloro, bromo and iodo groups; sulfonic ester groups, such as mesylate, tosylate, brosylate, nosylate, and the like; and acyloxy groups, such as acetoxy, trifluoroacetoxy, and the like.

Suitable inert diluents or solvents for use in these schemes include, by way of illustration and not limitation, tetrahydrofuran (THF), acetonitrile, N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), toluene, dichloromethane (DCM), chloroform (CHCl₃), and the like.

All reactions are typically conducted at a temperature within the range of about −78° C. to about 110° C., for example at room temperature. Reactions may be monitored by use of thin layer chromatography (TLC), high performance liquid chromatography (HPLC), and/or LCMS until completion. Reactions may be complete in minutes, may take hours, typically from 1-2 hours and up to 48 hours, or days, such as up to 3-4 days. Upon completion, the resulting mixture or reaction product may be further treated in order to obtain the desired product. For example, the resulting mixture or reaction product may be subjected to one or more of the following procedures: dilution (for example with saturated NaHCO₃); extraction (for example, with ethyl acetate, CHCl₃, DCM, aqueous HCl); washing (for example, with DCM, saturated aqueous NaCl, or saturated aqueous NaHCO₃); drying (for example, over MgSO₄ or Na₂SO₄, or in vacuo); filtration; being concentrated (for example, in vacuo); being redissolved (for example in a 1:1 acetic acid:H₂O solution); and/or purification (for example by preparative HPLC, reverse phase preparative HPLC, or crystallization).

By way of illustration, compounds of the invention can be prepared by one or more of the following schemes, which are detailed in the examples.

The starting material 1, for example, 4-(2-carboxyphenyl)piperidine-1-carboxylic acid t-butyl ester (P=Boc), is commercially available, and undergoes a borane reduction to form compound 2. Suitable reduction reagents include borane dimethyl sulfide complex, 9-borabicyclo[3.3.1]nonane, borane 1,2-bis(t-butylthio)ethane complex, borane t-butylamine complex, borane di(t-butyl)phosphine complex, borane-tetrahydrofuran complex and so forth. The next step involves converting the hydroxyl group of compound 2 into a leaving group. For example, Compound 2 can undergo tosylation with an appropriate reagent such as p-toluenesulfonyl chloride (TsCl) in a suitable base such as triethylenediamine, to form the tosylate ester, compound 3. See, for example, Hartung et al. (1997) Synthesis 12:1433-1438. Alternately, compound 2 can be combined with methanesulfonic anhydride in N,N-diisopropylethylamine.

The 2-fluorophenol compound 4 is coupled with compound 3 by nucleophilic displacement. The protected amine is then deprotected to yield a compound of the invention. Compound 4 is either commercially available, or is readily synthesized by techniques that are well known in the art.

Compounds of the invention may also be prepared using the Mitsunobu coupling reaction (Mitsunobu and Yamada (1967) M. Bull. Chem. Soc. JPN. 40:2380-2382), followed by deprotection of the amine. This reaction is typically conducted using standard Mitsunobu coupling conditions, using a redox system containing an azodicarboxylate such as diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD) and a phosphine catalyst such as triphenylphosphine (PPh₃).

The starting material, compound 5, can be synthesized as follows:

Compound 6 and compound 7 are coupled using Suzuki coupling reaction conditions to form compound 8. Representative catalysts include palladium and nickel catalysts, such as bis(triphenylphosphine)palladium(II), tetrakis(triphenylphosphine) palladium(0), [1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium(II), bis[1,2-bis(diphenylphosphino)propane]palladium(0), palladium(II) acetate, [1,1′-bis (diphenylphosphino)ferrocene]dichloronickel(II) and the like. Optionally, a base is employed in this reaction, such as sodium carbonate, sodium bicarbonate, potassium phosphate, triethylamine and the like. Compound 8 is hydrogenated, typically using Pearlman's Catalyst (wet Pd(OH)₂/C) to form compound 9, which then undergoes a borane reduction to form compound 5.

Starting materials 6 are 7 are either commercially available, or are readily synthesized by techniques that are well known in the art. Preferred leaving groups (L) include halogens and triflate, and examples of compound 6 include methyl 2-bromo-5-fluorobenzoate. Examples of compound 7 include 4-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-3,6-dihydro-2H-pyridine-1-carboxylic acid t-butyl ester.

If desired, pharmaceutically acceptable salts of the compounds of formula I or II can be prepared by contacting the free acid or base form of a compound of formula I or II, respectively, with a pharmaceutically acceptable base or acid.

Certain of the intermediates described herein are believed to be novel and accordingly, such compounds are provided as further aspects of the invention including, for example, compounds of formula III:

or a salt thereof, where P represents an amino-protecting group, particularly t-butoxycarbonyl (Boc) where a, R¹, and R³⁻⁶ are as defined for formulas I or II. In one embodiment of the invention, compounds of the invention can be prepared by deprotecting compounds of formula III to provide compounds of formula I or II, or a pharmaceutically acceptable salt thereof.

Further details regarding specific reaction conditions and other procedures for preparing representative compounds of the invention or intermediates thereof are described in the Examples set forth below.

Utility

Compounds of the invention possess serotonin and norepinephrine reuptake inhibitory activity. Thus, these compounds are expected to have therapeutic utility as combined serotonin and norepinephrine reuptake inhibitors (SNRIs). In one embodiment, compounds of the invention possess equal or approximately equal serotonin reuptake inhibitory activity and norepinephrine reuptake inhibitory activity.

The inhibition constant (K_(i)) of a compound is the concentration of competing ligand in a competition assay that would occupy 50% of the transporters if no radioligand were present. K_(i) values can be determined from radioligand competition binding studies with ³H-nisoxetine (for the norepinephrine transporter, NET) and ³H-citalopram (for the serotonin transporter, SERT), as described in Assay 1. These K_(i) values are derived from IC₅₀ values in the binding assay using the Cheng-Prusoff equation and the K_(d) of the radioligand (Cheng & Prusoff (1973) Biochem. Pharmacol. 22(23):3099-3108). Functional IC₅₀ values can be determined in the functional inhibition of uptake assays described in Assay 2. These IC₅₀ values can be converted to K_(i) values using the Cheng-Prusoff equation and the K_(m) of the transmitter for the transporter. It is noted however, that the uptake assay conditions described in Assay 2 are such that the IC₅₀ values are very close to the K_(i) values, should a mathematical conversion be desired, since the neurotransmitter concentration (5-HT or NE) used in the assay is well below its K_(m) for the respective transporter.

One measure of the affinity of a compound for SERT or NET is the inhibitory constant (pK_(i)) for binding to the transporter. The pK_(i) value is the negative logarithm to base 10 of the Compounds of the invention of particular interest are those having a pK_(i) at SERT greater than or equal to about 7.5, and in one particular embodiment greater than or equal to about 7.9. Compounds of the invention of particular interest also include those having a pK_(i) at NET greater than or equal to about 7.5, and in one particular embodiment greater than or equal to about 8.0. In another embodiment, compounds of interest have a pK_(i) at NET within the range of 8.0 to 9.0. In another embodiment, compounds of interest have a pK_(i) at SERT greater than or equal to about 7.9 and a pK_(i) at NET of greater than or equal to about 8.0. In another embodiment, compounds of interest have a pK_(i) at SERT and at NET greater than or equal to about 8.0. Such values can be determined by techniques that are well known in the art, as well as in the assays described herein.

In one embodiment, compounds of the invention exhibit a NET pK_(i)≧8 and: a SERT K_(i)/NET K_(i) in the range of 0.1 to 100; a SERT K_(i)/NET K_(i) in the range of 0.3 to 100; a SERT K_(i)/NET K_(i) in the range of 0.3 to 10; or a SERT K_(i)/NET K_(i) in the range of 0.1 to 30. In another embodiment, compounds of the invention exhibit a NET pK_(i)≧9 and: a SERT K_(i)/NET K_(i) in the range of 0.1 to 100; a SERT K_(i)/NET K_(i) in the range of 0.3 to 100; a SERT K_(i)/NET K_(i) in the range of 0.3 to 10; or a SERT K_(i)/NET K_(i) in the range of 0.1 to 30.

Another measure of serotonin and norepinephrine reuptake inhibition is the pIC₅₀ value. In one embodiment, compounds of interest have a serotonin reuptake inhibition pIC₅₀ value of greater than or equal to about 7.0 and a norepinephrine reuptake inhibition pIC₅₀ value of greater than or equal to about 7.0; and in another embodiment, compounds of interest have a serotonin reuptake inhibition pIC₅₀ value of greater than or equal to about 7.5 and a norepinephrine reuptake inhibition pIC₅₀ value of greater than or equal to about 7.5. In one particular embodiment, the compounds have a serotonin reuptake inhibition pIC₅₀ value of greater than or equal to about 8.0 and a norepinephrine reuptake inhibition pIC₅₀ value of greater than or equal to about 8.0. In one particular embodiment, the compounds of the invention have balanced pIC₅₀ values, i.e., have the same pIC₅₀ value at both SERT and NET±0.6.

In another embodiment, compounds of the invention are selective for inhibition of SERT and NET over the dopamine transporter (DAT). For example in this embodiment, compounds of particular interest are those that exhibit a binding affinity for SERT and NET that is at least 5 times higher than the binding affinity for DAT, or that is at least 10 times higher than for DAT, or at least 20 or 30 times higher than for DAT. In another embodiment, the compounds do not exhibit significant DAT inhibition. In still another embodiment, the compounds exhibit less than 50% inhibition of DAT activity when measured at a concentration of 794 nM. Under the assay conditions used, a compound which exhibits ≦50% inhibition would have an estimated pK_(i) value at DAT of ≦6.1.

In still another embodiment, compounds of the invention possess dopamine reuptake inhibitory activity as well as SERT and NET activity. For example in this embodiment, compounds of particular interest are those that exhibit a pK_(i) at SERT and NET greater than or equal to about 7.5, and a pK_(i) at DAT greater than or equal to about 7.0.

It is noted that in some cases, compounds of the invention may possess either weak serotonin reuptake inhibitory activity or weak norepinephrine reuptake inhibitory activity. In these cases, those of ordinary skill in the art will recognize that such compounds still have utility as primarily either a NET inhibitor or a SERT inhibitor, respectively, or will have utility as research tools.

Exemplary assays to determine the serotonin and/or norepinephrine reuptake inhibiting activity of compounds of the invention include by way of illustration and not limitation, assays that measure SERT and NET binding, for example, as described in Assay 1. In addition, it is useful to understand the level of DAT binding and uptake in an assay such as that described in Assay 1. Useful secondary assays include neurotransmitter uptake assays to measure competitive inhibition of serotonin and norepinephrine uptake into cells expressing the respective human or rat recombinant transporter (hSERT, hNET, or hDAT) as described in Assay 2, and ex vivo radioligand binding and neurotransmitter uptake assays that are used to determine the in vivo occupancy of SERT, NET and DAT in tissue as described in Assay 3. Other assays that are useful to evaluate pharmacological properties of test compounds include those listed in Assay 4. Exemplary in vivo assays include the formalin paw test described in Assay 5, which is a reliable predictor of clinical efficacy for the treatment of neuropathic pain, and the spinal nerve ligation model described in Assay 6. The aforementioned assays are useful in determining the therapeutic utility, for example, the neuropathic pain relieving activity, of compounds of the invention. Other properties and utilities of compounds of the invention can be demonstrated using various in vitro and in vivo assays well-known to those skilled in the art.

Compounds of the invention are expected to be useful for the treatment and/or prevention of medical conditions in which the regulation of monoamine transporter function is implicated, in particular those conditions mediated by or responsive to the inhibition of serotonin and norepinephrine reuptake. Thus it is expected that patients suffering from a disease or disorder that is treated by the inhibition of the serotonin and/or the norepinephrine transporter can be treated by administering a therapeutically effective amount of a serotonin and norepinephrine reuptake inhibitor of the invention. Such medical conditions include, by way of example: pain disorders such as neuropathic pain, fibromyalgia, and chronic pain; depressive disorders such as major depression; affective disorders such as an anxiety disorder; attention deficit hyperactivity disorder; cognitive disorders such as dementia; stress urinary incontinence; chronic low back pain; and osteoarthritis.

The amount of active agent administered per dose or the total amount administered per day may be predetermined or it may be determined on an individual patient basis by taking into consideration numerous factors, including the nature and severity of the patient's condition, the condition being treated, the age, weight, and general health of the patient, the tolerance of the patient to the active agent, the route of administration, pharmacological considerations such as the activity, efficacy, pharmacokinetics and toxicology profiles of the active agent and any secondary agents being administered, and the like. Treatment of a patient suffering from a disease or medical condition (such as neuropathic pain) can begin with a predetermined dosage or a dosage determined by the treating physician, and will continue for a period of time necessary to prevent, ameliorate, suppress, or alleviate the symptoms of the disease or medical condition. Patients undergoing such treatment will typically be monitored on a routine basis to determine the effectiveness of therapy. For example, in treating neuropathic pain, a measure of the effectiveness of treatment may involve assessment of the patient's quality of life, e.g., improvements in the patient's sleeping patterns, work attendance, ability to exercise and be ambulatory, etc. Pain scales, operating on a point basis, may also be used to help evaluate a patient's pain level. Indicators for the other diseases and conditions described herein, are well-known to those skilled in the art, and are readily available to the treating physician. Continuous monitoring by the physician will insure that the optimal amount of active agent will be administered at any given time, as well as facilitating the determination of the duration of treatment. This is of particular value when secondary agents are also being administered, as their selection, dosage, and duration of therapy may also require adjustment. In this way, the treatment regimen and dosing schedule can be adjusted over the course of therapy so that the lowest amount of active agent that exhibits the desired effectiveness is administered and, further, that administration is continued only so long as is necessary to successfully treat the disease or medical condition.

Pain Disorders

SNRIs have been shown to have a beneficial effect on pain such as painful diabetic neuropathy (duloxetine, Goldstein et al. (2005) Pain 116:109-118; venlafaxine, Rowbotham et al. (2004) Pain 110:697-706), fibromyalgia (duloxetine, Russell et al. (2008) Pain 136(3):432-444; milnacipran, Vitton et al. (2004) Human Psychopharmacology 19:S27-S35), and migraine (venlafaxine, Ozyalcin et al. (2005) Headache 45(2):144-152). Thus, one embodiment of the invention relates to a method for treating a pain disorder, comprising administering to a patient a therapeutically effective amount of a compound of the invention. Typically, the therapeutically effective amount will be the amount that is sufficient to relieve the pain. Exemplary pain disorders include, by way of illustration, acute pain, persistent pain, chronic pain, inflammatory pain, and neuropathic pain. More specifically, these include pain associated with or caused by: arthritis; back pain including chronic low back pain; cancer, including tumor related pain (e.g., bone pain, headache, facial pain or visceral pain) and pain associated with cancer therapy (e.g., post-chemotherapy syndrome, chronic post-surgical pain syndrome and post-radiation syndrome); carpal tunnel syndrome; fibromyalgia; headaches including chronic tension headaches; inflammation associated with polymyalgia, rheumatoid arthritis and osteoarthritis; migraine; neuropathic pain including complex regional pain syndrome; overall pain; post-operative pain; shoulder pain; central pain syndromes, including post-stroke pain, and pain associated with spinal cord injuries and multiple sclerosis; phantom limb pain; pain associated with Parkinson's disease; and visceral pain (e.g., irritable bowel syndrome). Of particular interest is the treatment of neuropathic pain, which includes diabetic peripheral neuropathy (DPN), HIV-related neuropathy, post-herpetic neuralgia (PHN), and chemotherapy-induced peripheral neuropathy. When used to treat pain disorders such as neuropathic pain, compounds of the invention may be administered in combination with other therapeutic agents, including anticonvulsants, antidepressants, muscle relaxants, NSAIDs, opioid agonists, opioid antagonists, selective serotonin reuptake inhibitors, sodium channel blockers, and sympatholytics. Exemplary compounds within these classes are described herein.

Depressive Disorders

Another embodiment of the invention relates to a method of treating a depressive disorder, comprising administering to a patient a therapeutically effective amount of a compound of the invention. Typically, the therapeutically effective amount will be the amount that is sufficient to alleviate depression and provide a sense of general well-being. Exemplary depressive disorders include, by way of illustration and not limitation: depression associated with Alzheimer's disease, bipolar disorder, cancer, child abuse, infertility, Parkinson's disease, postmyocardial infarction, and psychosis; dysthymia; grumpy or irritable old man syndrome; induced depression; major depression; pediatric depression; postmenopausal depression; post partum depression; recurrent depression; single episode depression; and subsyndromal symptomatic depression. Of particular interest is the treatment of major depression. When used to treat depressive disorders, compounds of the invention may be administered in combination with other therapeutic agents, including antidepressants and dual serotonin-norepinephrine reuptake inhibitors. Exemplary compounds within these classes are described herein.

Affective Disorders

Another embodiment of the invention relates to a method of treating an affective disorder, comprising administering to a patient a therapeutically effective amount of a compound of the invention. Exemplary affective disorders include, by way of illustration and not limitation: anxiety disorders such as general anxiety disorder; avoidant personality disorder; eating disorders such as anorexia nervosa, bulimia nervosa and obesity; obsessive compulsive disorder; panic disorder; personality disorders such as avoidant personality disorder and attention deficit hyperactivity disorder (ADHD); post-traumatic stress syndrome; phobias such as agoraphobia, as well as simple and other specific phobias, and social phobia; premenstrual syndrome; psychotic disorders, such as schizophrenia and mania; seasonal affective disorder; sexual dysfunction, including premature ejaculation, male impotence, and female sexual dysfunction such as female sexual arousal disorder; social anxiety disorder; and substance abuse disorders, including chemical dependencies such as addictions to alcohol, benzodiazepines, cocaine, heroin, nicotine and phenobarbital, as well as withdrawal syndromes that may arise from these dependencies. When used to treat affective disorders, compounds of the invention may be administered in combination with other therapeutic agents, including antidepressants. Exemplary compounds within these classes are described herein.

Atomoxetine, which is 10-fold NET selective, is approved for attention deficit hyperactivity disorder (ADHD) therapy, and clinical studies have shown that the SNRI, venlafaxine, can also have a beneficial effect in treating ADHD (Mukaddes et al. (2002) Eur. Neuropsychopharm. 12(Supp 3):421). Thus, the compounds of the invention are also expected to be useful in methods for treating attention deficit hyperactivity disorder by administering to a patient a therapeutically effective amount of a compound of the invention. When used to treat depression, compounds of the invention may be administered in combination with other therapeutic agents, including antidepressants. Exemplary compounds within these classes are described herein.

Cognitive Disorders

Another embodiment of the invention relates to a method of treating a cognitive disorder, comprising administering to a patient a therapeutically effective amount of a compound of the invention. Exemplary cognitive disorders include, by way of illustration and not limitation: dementia, which includes degenerative dementia (e.g., Alzheimer's disease, Creutzfeldt-Jakob disease, Huntingdon's chorea, Parkinson's disease, Pick's disease, and senile dementia), vascular dementia (e.g., multi-infarct dementia), and dementia associated with intracranial space occupying lesions, trauma, infections and related conditions (including HIV infection), metabolism, toxins, anoxia and vitamin deficiency; and mild cognitive impairment associated with ageing, such as age associated memory impairment, amnesiac disorder and age-related cognitive decline. When used to treat cognitive disorders, compounds of the invention may be administered in combination with other therapeutic agents, including anti-Alzheimer's agents and anti-Parkinson's agents. Exemplary compounds within these classes are described herein.

Other Disorders

SNRIs have also been shown to be effective for the treatment of stress urinary incontinence (Dmochowski (2003) Journal of Urology 170(4): 1259-1263). Thus, another embodiment of the invention relates to a method for treating stress urinary incontinence, comprising administering to a patient a therapeutically effective amount of a compound of the invention. When used to treat stress urinary incontinence, compounds of the invention may be administered in combination with other therapeutic agents, including anticonvulsants. Exemplary compounds within these classes are described herein.

Duloxetine, an SNRI, is undergoing clinical trials for evaluating its efficacy in treating chronic fatigue syndrome, and has recently been shown to be effective in treating fibromyalgia (Russell et al. (2008) Pain 136(3):432-444). The compounds of the invention, due to their ability to inhibit SERT and NET, are also expected to have this utility, and another embodiment of the invention relates to a method for treating chronic fatigue syndrome, comprising administering to a patient a therapeutically effective amount of a compound of the invention.

Sibutramine, a norepinephrine and dopamine reuptake inhibitor, has been shown to be useful in treating obesity (Wirth et al. (2001) JAMA 286(11):1331-1339). The compounds of the invention, due to their ability to inhibit NET, are also expected to have this utility, and another embodiment of the invention relates to a method for treating obesity, comprising administering to a patient a therapeutically effective amount of a compound of the invention.

Desvenlafaxine, an SNRI, has been shown to relieve vasomotor symptoms associated with menopause (Deecher et al. (2007) Endocrinology 148(3):1376-1383). The compounds of the invention, due to their ability to inhibit SERT and NET, are also expected to have this utility, and another embodiment of the invention relates to a method for treating vasomotor symptoms associated with menopause, comprising administering to a patient a therapeutically effective amount of a compound of the invention.

Research Tools

Since compounds of the invention possess both serotonin reuptake inhibition activity and norepinephrine reuptake inhibition activity, such compounds are also useful as research tools for investigating or studying biological systems or samples having serotonin or norepinephrine transporters. Any suitable biological system or sample having serotonin and/or norepinephrine transporters may be employed in such studies which may be conducted either in vitro or in vivo. Representative biological systems or samples suitable for such studies include, but are not limited to, cells, cellular extracts, plasma membranes, tissue samples, isolated organs, mammals (such as mice, rats, guinea pigs, rabbits, dogs, pigs, humans, and so forth), and the like, with mammals being of particular interest. In one particular embodiment of the invention, serotonin reuptake in a mammal is inhibited by administering a serotonin reuptake-inhibiting amount of a compound of the invention. In another particular embodiment, norepinephrine reuptake in a mammal is inhibited by administering a norepinephrine reuptake-inhibiting amount of a compound of the invention. Compounds of the invention can also be used as research tools by conducting biological assays using such compounds.

When used as a research tool, a biological system or sample comprising a serotonin transporter and/or a norepinephrine transporter is typically contacted with a serotonin reuptake-inhibiting or norepinephrine reuptake-inhibiting amount of a compound of the invention. After the biological system or sample is exposed to the compound, the effects of inhibiting serotonin reuptake and/or norepinephrine reuptake are determined using conventional procedures and equipment. Exposure encompasses contacting cells or tissue with the compound, administering the compound to a mammal, for example by i.p. or i.v. administration, and so forth. This determining step may comprise measuring a response, i.e., a quantitative analysis or may comprise an observation, i.e., a qualitative analysis. Measuring a response involves, for example, determining the effects of the compound on the biological system or sample using conventional procedures and equipment, such as serotonin and norepinephrine reuptake assays. The assay results can be used to determine the activity level as well as the amount of compound necessary to achieve the desired result, i.e., a serotonin reuptake-inhibiting and a norepinephrine reuptake-inhibiting amount.

Additionally, compounds of the invention can be used as research tools for evaluating other chemical compounds, and thus are also useful in screening assays to discover, for example, new compounds having both serotonin reuptake-inhibiting activity and norepinephrine reuptake-inhibiting activity. In this manner, compounds of the invention are used as standards in an assay to allow comparison of the results obtained with a test compound and with compounds of the invention to identify those test compounds that have about equal or superior reuptake-inhibiting activity, if any. For example, reuptake data for a test compound or a group of test compounds is compared to the reuptake data for a compound of the invention to identify those test compounds that have the desired properties, e.g., test compounds having reuptake-inhibiting activity about equal or superior to a compound of the invention, if any. This aspect of the invention includes, as separate embodiments, both the generation of comparison data (using the appropriate assays) and the analysis of the test data to identify test compounds of interest. Thus, a test compound can be evaluated in a biological assay, by a method comprising the steps of: (a) conducting a biological assay with a test compound to provide a first assay value; (b) conducting the biological assay with a compound of the invention to provide a second assay value; wherein step (a) is conducted either before, after or concurrently with step (b); and (c) comparing the first assay value from step (a) with the second assay value from step (b). Exemplary biological assays include serotonin and norepinephrine reuptake assays.

Pharmaceutical Compositions and Formulations

Compounds of the invention are typically administered to a patient in the form of a pharmaceutical composition or formulation. Such pharmaceutical compositions may be administered to the patient by any acceptable route of administration including, but not limited to, oral, rectal, vaginal, nasal, inhaled, topical (including transdermal) and parenteral modes of administration. Further, the compounds of the invention may be administered, for example orally, in multiple doses per day (e.g., twice, three times or four times daily), in a single daily dose, in a twice daily dose, in a single weekly dose, and so forth. It will be understood that any form of the compounds of the invention, (i.e., free base, pharmaceutically acceptable salt, solvate, etc.) that is suitable for the particular mode of administration can be used in the pharmaceutical compositions discussed herein.

Accordingly, in one embodiment, the invention relates to a pharmaceutical composition comprising a pharmaceutically acceptable carrier and a compound of the invention. The compositions may contain other therapeutic and/or formulating agents if desired. When discussing compositions, the “compound of the invention” may also be referred to herein as the “active agent,” to distinguish it from other components of the formulation, such as the carrier. Thus, it is understood that the term “active agent” includes compounds of formula I as well as pharmaceutically acceptable salts and solvates of that compound.

Pharmaceutical compositions of the invention typically contain a therapeutically effective amount of a compound of the invention. Those skilled in the art will recognize, however, that a pharmaceutical composition may contain more than a therapeutically effective amount, i.e., bulk compositions, or less than a therapeutically effective amount, i.e., individual unit doses designed for multiple administration to achieve a therapeutically effective amount. Typically, the composition will contain from about 0.01-95 wt % of active agent, including, from about 0.01-30 wt %, such as from about 0.01-10 wt %, with the actual amount depending upon the formulation itself, the route of administration, the frequency of dosing, and so forth. In one embodiment, a composition suitable for an oral dosage form, for example, may contain about 5-70 wt %, or from about 10-60 wt % of active agent. In one exemplary embodiment, a pharmaceutical composition contains from about 1 to 20 mg of active agent, including from about 1 to 15 mg of active agent and from about 1 to 10 mg of active agent. In another exemplary embodiment, a pharmaceutical composition contains from about 5 to 20 mg of active agent, including from about 7.5 to 15 mg of active agent. For example the active agent may be formulated in 1 mg and 10 mg unit doses.

Any conventional carrier or excipient may be used in the pharmaceutical compositions of the invention. The choice of a particular carrier or excipient, or combinations of carriers or excipients, will depend on the mode of administration being used to treat a particular patient or type of medical condition or disease state. In this regard, the preparation of a suitable composition for a particular mode of administration is well within the scope of those skilled in the pharmaceutical arts. Additionally, carriers or excipients used in such compositions are commercially available. By way of further illustration, conventional formulation techniques are described in Remington: The Science and Practice of Pharmacy, 20^(th) Edition, Lippincott Williams & White, Baltimore, Md. (2000); and H. C. Ansel et al., Pharmaceutical Dosage Forms and Drug Delivery Systems, 7^(th) Edition, Lippincott Williams & White, Baltimore, Md. (1999).

Representative examples of materials which can serve as pharmaceutically acceptable carriers include, but are not limited to, the following: sugars, such as lactose, glucose and sucrose; starches, such as corn starch and potato starch; cellulose, such as microcrystalline cellulose, and its derivatives, such as sodium carboxymethyl cellulose, ethyl cellulose and cellulose acetate; powdered tragacanth; malt; gelatin; talc; excipients, such as cocoa butter and suppository waxes; oils, such as peanut oil, cottonseed oil, safflower oil, sesame oil, olive oil, corn oil and soybean oil; glycols, such as propylene glycol; polyols, such as glycerin, sorbitol, mannitol and polyethylene glycol; esters, such as ethyl oleate and ethyl laurate; agar; buffering agents, such as magnesium hydroxide and aluminum hydroxide; alginic acid; pyrogen-free water; isotonic saline; Ringer's solution; ethyl alcohol; phosphate buffer solutions; compressed propellant gases, such as chlorofluorocarbons and hydrofluorocarbons; and other non-toxic compatible substances employed in pharmaceutical compositions.

Pharmaceutical compositions are typically prepared by thoroughly and intimately mixing or blending the active agent with a pharmaceutically acceptable carrier and one or more optional ingredients. The resulting uniformly blended mixture may then be shaped or loaded into tablets, capsules, pills, canisters, cartridges, dispensers, and the like, using conventional procedures and equipment.

In one embodiment, the pharmaceutical compositions are suitable for oral administration. One exemplary dosing regimen would be an oral dosage form administered once or twice daily. Suitable compositions for oral administration may be in the form of capsules, tablets, pills, lozenges, cachets, dragees, powders, granules; solutions or suspensions in an aqueous or non-aqueous liquid; oil-in-water or water-in-oil liquid emulsions; elixirs or syrups; and the like; each containing a predetermined amount of the active agent.

When intended for oral administration in a solid dosage form (i.e., as capsules, tablets, pills, and the like), the composition will typically comprise the active agent and one or more pharmaceutically acceptable carriers, such as sodium citrate or dicalcium phosphate. Solid dosage forms may also comprise: fillers or extenders, such as starches, microcrystalline cellulose, lactose, sucrose, glucose, mannitol, and/or silicic acid; binders, such as carboxymethylcellulose, alginates, gelatin, polyvinyl pyrrolidone, sucrose and/or acacia; humectants, such as glycerol; disintegrating agents, such as agar-agar, calcium carbonate, potato or tapioca starch, alginic acid, certain silicates, and/or sodium carbonate; solution retarding agents, such as paraffin; absorption accelerators, such as quaternary ammonium compounds; wetting agents, such as cetyl alcohol and/or glycerol monostearate; absorbents, such as kaolin and/or bentonite clay; lubricants, such as talc, calcium stearate, magnesium stearate, solid polyethylene glycols, sodium lauryl sulfate, and/or mixtures thereof; coloring agents; and buffering agents.

Release agents, wetting agents, coating agents, sweetening, flavoring and perfuming agents, preservatives and antioxidants may also be present in the pharmaceutical compositions. Exemplary coating agents for tablets, capsules, pills and like, include those used for enteric coatings, such as cellulose acetate phthalate, polyvinyl acetate phthalate, hydroxypropyl methylcellulose phthalate, methacrylic acid-methacrylic acid ester copolymers, cellulose acetate trimellitate, carboxymethyl ethyl cellulose, hydroxypropyl methyl cellulose acetate succinate, and the like. Examples of pharmaceutically acceptable antioxidants include: water-soluble antioxidants, such as ascorbic acid, cysteine hydrochloride, sodium bisulfate, sodium metabisulfate, sodium sulfite, and the like; oil-soluble antioxidants, such as ascorbyl palmitate, butylated hydroxyanisole, butylated hydroxytoluene, lecithin, propyl gallate, alpha-tocopherol, and the like; and metal-chelating agents, such as citric acid, ethylenediamine tetraacetic acid, sorbitol, tartaric acid, phosphoric acid, and the like.

Compositions may also be formulated to provide slow or controlled release of the active agent using, by way of example, hydroxypropyl methyl cellulose in varying proportions or other polymer matrices, liposomes and/or microspheres. In addition, the pharmaceutical compositions of the invention may contain opacifying agents and may be formulated so that they release the active agent only, or preferentially, in a certain portion of the gastrointestinal tract, optionally, in a delayed manner. Examples of embedding compositions which can be used include polymeric substances and waxes. The active agent can also be in micro-encapsulated form, if appropriate, with one or more of the above-described excipients.

Suitable liquid dosage forms for oral administration include, by way of illustration, pharmaceutically acceptable emulsions, microemulsions, solutions, suspensions, syrups and elixirs. Liquid dosage forms typically comprise the active agent and an inert diluent, such as, for example, water or other solvents, solubilizing agents and emulsifiers, such as ethyl alcohol, isopropyl alcohol, ethyl carbonate, ethyl acetate, benzyl alcohol, benzyl benzoate, propylene glycol, 1,3-butylene glycol, oils (e.g., cottonseed, groundnut, corn, germ, olive, castor and sesame oils), glycerol, tetrahydrofuryl alcohol, polyethylene glycols and fatty acid esters of sorbitan, and mixtures thereof. Suspensions may contain suspending agents such as, for example, ethoxylated isostearyl alcohols, polyoxyethylene sorbitol and sorbitan esters, microcrystalline cellulose, aluminium metahydroxide, bentonite, agar-agar and tragacanth, and mixtures thereof.

When intended for oral administration, the pharmaceutical compositions of the invention may be packaged in a unit dosage form. The term “unit dosage form” refers to a physically discrete unit suitable for dosing a patient, i.e., each unit containing a predetermined quantity of the active agent calculated to produce the desired therapeutic effect either alone or in combination with one or more additional units. For example, such unit dosage forms may be capsules, tablets, pills, and the like.

In another embodiment, the compositions of the invention are suitable for inhaled administration, and will typically be in the form of an aerosol or a powder. Such compositions are generally administered using well-known delivery devices, such as a nebulizer, dry powder, or metered-dose inhaler. Nebulizer devices produce a stream of high velocity air that causes the composition to spray as a mist that is carried into a patient's respiratory tract. An exemplary nebulizer formulation comprises the active agent dissolved in a carrier to form a solution, or micronized and combined with a carrier to form a suspension of micronized particles of respirable size. Dry powder inhalers administer the active agent as a free-flowing powder that is dispersed in a patient's air-stream during inspiration. An exemplary dry powder formulation comprises the active agent dry-blended with an excipient such as lactose, starch, mannitol, dextrose, polylactic acid, polylactide-co-glycolide, and combinations thereof. Metered-dose inhalers discharge a measured amount of the active agent using compressed propellant gas. An exemplary metered-dose formulation comprises a solution or suspension of the active agent in a liquefied propellant, such as a chlorofluorocarbon or hydrofluoroalkane. Optional components of such formulations include co-solvents, such as ethanol or pentane, and surfactants, such as sorbitan trioleate, oleic acid, lecithin, and glycerin. Such compositions are typically prepared by adding chilled or pressurized hydrofluoroalkane to a suitable container containing the active agent, ethanol (if present) and the surfactant (if present). To prepare a suspension, the active agent is micronized and then combined with the propellant. Alternatively, a suspension formulation can be prepared by spray drying a coating of surfactant on micronized particles of the active agent. The formulation is then loaded into an aerosol canister, which forms a portion of the inhaler.

Compounds of the invention can also be administered parenterally (e.g., by subcutaneous, intravenous, intramuscular, or intraperitoneal injection). For such administration, the active agent is provided in a sterile solution, suspension, or emulsion. Exemplary solvents for preparing such formulations include water, saline, low molecular weight alcohols such as propylene glycol, polyethylene glycol, oils, gelatin, fatty acid esters such as ethyl oleate, and the like. A typical parenteral formulation is a sterile pH 4-7 aqueous solution of the active agent. Parenteral formulations may also contain one or more solubilizers, stabilizers, preservatives, wetting agents, emulsifiers, and dispersing agents. These formulations may be rendered sterile by use of a sterile injectable medium, a sterilizing agent, filtration, irradiation, or heat.

Compounds of the invention can also be administered transdermally using known transdermal delivery systems and excipients. For example, the compound can be admixed with permeation enhancers, such as propylene glycol, polyethylene glycol monolaurate, azacycloalkan-2-ones, and the like, and incorporated into a patch or similar delivery system. Additional excipients including gelling agents, emulsifiers and buffers, may be used in such transdermal compositions if desired.

If desired, compounds of the invention may be administered in combination with one or more other therapeutic agents. Thus, in one embodiment, compositions of the invention may optionally contain other drugs that are co-administered with a compound of the invention. For example, the composition may further comprise one or more drugs (also referred to as “secondary agents(s)”) selected from the group of anti-Alzheimer's agents, anticonvulsants (antiepileptics), antidepressants, anti-Parkinson's agents, dual serotonin-norepinephrine reuptake inhibitors (SNRIs), non-steroidal anti-inflammatory agents (NSAIDs), norepinephrine reuptake inhibitors, opioid agonists (opioid analgesics), opioid antagonists, selective serotonin reuptake inhibitors, sodium channel blockers, sympatholytics, and combinations thereof. Numerous examples of such therapeutic agents are well known in the art, and examples are described herein. By combining a compound of the invention with a secondary agent, triple therapy can be achieved, i.e., serotonin reuptake inhibitory activity, norepinephrine reuptake inhibitory activity, and activity associated with the secondary agent (e.g., antidepressant activity), using only two active components. Since pharmaceutical compositions containing two active components are typically easier to formulate than compositions containing three active components, such two-component compositions provide a significant advantage over compositions containing three active components. Accordingly, in yet another aspect of the invention, a pharmaceutical composition comprises a compound of the invention, a second active agent, and a pharmaceutically acceptable carrier. Third, fourth, etc., active agents may also be included in the composition. In combination therapy, the amount of compound of the invention that is administered, as well as the amount of secondary agents, may be less than the amount typically administered in monotherapy.

A compound of the invention may be either physically mixed with the second active agent to form a composition containing both agents; or each agent may be present in separate and distinct compositions which are administered to the patient simultaneously or sequentially. For example, a compound of the invention can be combined with a second active agent using conventional procedures and equipment to form a combination of active agents comprising a compound of the invention and a second active agent. Additionally, the active agents may be combined with a pharmaceutically acceptable carrier to form a pharmaceutical composition comprising a compound of the invention, a second active agent and a pharmaceutically acceptable carrier. In this embodiment, the components of the composition are typically mixed or blended to create a physical mixture. The physical mixture is then administered in a therapeutically effective amount using any of the routes described herein.

Alternatively, the active agents may remain separate and distinct before administration to the patient. In this embodiment, the agents are not physically mixed together before administration but are administered simultaneously or at separate times as separate compositions. Such compositions can be packaged separately or may be packaged together in a kit. When administered at separate times, the secondary agent will typically be administered less than 24 hours after administration of the compound of the invention, ranging anywhere from concurrent with administration of the compound of the invention to about 24 hours post-dose. This is also referred to as sequential administration. Thus, a compound of the invention can be orally administered simultaneously or sequentially with another active agent using two tablets, with one tablet for each active agent, where sequential may mean being administered immediately after administration of the compound of the invention or at some predetermined time later (e.g., one hour later or three hours later). Alternatively, the combination may be administered by different routes of administration, i.e., one orally and the other by inhalation.

In one embodiment, the kit comprises a first dosage form comprising a compound of the invention and at least one additional dosage form comprising one or more of the secondary agents set forth herein, in quantities sufficient to carry out the methods of the invention. The first dosage form and the second (or third, etc.) dosage form together comprise a therapeutically effective amount of active agents for the treatment or prevention of a disease or medical condition in a patient.

Secondary agent(s), when included, are present in a therapeutically effective amount, i.e., are typically administered in an amount that produces a therapeutically beneficial effect when co-administered with a compound of the invention. The secondary agent can be in the form of a pharmaceutically acceptable salt, solvate, optically pure stereoisomer, and so forth. Thus, secondary agents listed below are intended to include all such forms, and are commercially available or can be prepared using conventional procedures and reagents.

Representative anti-Alzheimer's agents include, but are not limited to: donepezil, galantamine, memantine, rivastigmine, selegiline, tacrine, and combinations thereof.

Representative anticonvulsants (antiepileptics) include, but are not limited to: acetazolamide, albutoin, 4-amino-3-hydroxybutyric acid, beclamide, carbamazepine, cinromide, clomethiazole, clonazepam, diazepam, dimethadione, eterobarb, ethadione, ethosuximide, ethotoin, felbamate, fosphenyloin, gabapentin, lacosamide, lamotrigine, lorazepam, magnesium bromide, magnesium sulfate, mephenyloin, mephobarbital, methsuximide, midazolam, nitrazepam, oxazepam, oxcarbazepine, paramethadione, phenacemide, pheneturide, phenobarbital, phensuximide, phenyloin, potassium bromide, pregabalin, primidone, progabide, sodium bromide, sodium valproate, sulthiame, tiagabine, topiramate, trimethadione, valproic acid, valpromide, vigabatrin, zonisamide, and combinations thereof. In a particular embodiment, the anticonvulsant is selected from carbamazepine, gabapentin, pregabalin, and combinations thereof.

Representative antidepressants include, but are not limited to: adinazolam, amitriptyline, clomipramine, desipramine, dothiepin (e.g., dothiepin hydrochloride), doxepin, imipramine, lofepramine, mirtazapine, nortriptyline, protriptyline, trimipramine, venlafaxine, zimelidine, and combinations thereof.

Representative anti-Parkinson's agents include, but are not limited to: amantadine, apomorphine, benztropine, bromocriptine, carbidopa, diphenhydramine, entacapone, levodopa, pergolide, pramipexole, ropinirole, selegiline, tolcapone, trihexyphenidyl, and combinations thereof.

Representative dual serotonin-norepinephrine reuptake inhibitors (SNRIs) include, but are not limited to: bicifadine, desvenlafaxine, duloxetine, milnacipran, nefazodone, venlafaxine, and combinations thereof.

Representative non-steroidal anti-inflammatory agents (NSAIDs) include, but are not limited to: acemetacin, acetaminophen, acetyl salicylic acid, alclofenac, alminoprofen, amfenac, amiprilose, amoxiprin, anirolac, apazone, azapropazone, benorilate, benoxaprofen, bezpiperylon, broperamole, bucloxic acid, carprofen, clidanac, diclofenac, diflunisal, diftalone, enolicam, etodolac, etoricoxib, fenbufen, fenclofenac, fenclozic acid, fenoprofen, fentiazac, feprazone, flufenamic acid, flufenisal, fluprofen, flurbiprofen, furofenac, ibufenac, ibuprofen, indomethacin, indoprofen, isoxepac, isoxicam, ketoprofen, ketorolac, lofemizole, lornoxicam, meclofenamate, meclofenamic acid, mefenamic acid, meloxicam, mesalamine, miroprofen, mofebutazone, nabumetone, naproxen, niflumic acid, nimesulide, nitroflurbiprofen, olsalazine, oxaprozin, oxpinac, oxyphenbutazone, phenylbutazone, piroxicam, pirprofen, pranoprofen, salsalate, sudoxicam, sulfasalazine, sulindac, suprofen, tenoxicam, tiopinac, tiaprofenic acid, tioxaprofen, tolfenamic acid, tolmetin, triflumidate, zidometacin, zomepirac, and combinations thereof. In a particular embodiment, the NSAID is selected from etodolac, flurbiprofen, ibuprofen, indomethacin, ketoprofen, ketorolac, meloxicam, naproxen, oxaprozin, piroxicam, and combinations thereof. In a particular embodiment, the NSAID is selected from ibuprofen, indomethacin, nabumetone, naproxen (for example, naproxen sodium), and combinations thereof.

Representative muscle relaxants include, but are not limited to: carisoprodol, chlorzoxazone, cyclobenzaprine, diflunisal, metaxalone, methocarbamol, and combinations thereof.

Representative norepinephrine reuptake inhibitors include, but are not limited to: atomoxetine, buproprion and the buproprion metabolite hydroxybuproprion, maprotiline, reboxetine (for example, (S,S)-reboxetine), viloxazine, and combinations thereof. In a particular embodiment, the norepinephrine reuptake inhibitor is selected from atomoxetine, reboxetine, and combinations thereof.

Representative opioid agonists (opioid analgesics) and antagonists include, but are not limited to: buprenorphine, butorphanol, codeine, dihydrocodeine, fentanyl, hydrocodone, hydromorphone, levallorphan, levorphanol, meperidine, methadone, morphine, nalbuphine, nalmefene, nalorphine, naloxone, naltrexone, nalorphine, oxycodone, oxymorphone, pentazocine, propoxyphene, tramadol, and combinations thereof. In certain embodiments, the opioid agonist is selected from codeine, dihydrocodeine, hydrocodone, hydromorphone, morphine, oxycodone, oxymorphone, tramadol, and combinations thereof.

Representative selective serotonin reuptake inhibitors (SSRIs) include, but are not limited to: citalopram and the citalopram metabolite desmethylcitalopram, dapoxetine, escitalopram (e.g., escitalopram oxalate), fluoxetine and the fluoxetine desmethyl metabolite norfluoxetine, fluvoxamine (e.g., fluvoxamine maleate), paroxetine, sertraline and the sertraline metabolite demethylsertraline, and combinations thereof. In certain embodiments, the SSRI is selected from citalopram, paroxetine, sertraline, and combinations thereof.

Representative sodium channel blockers include, but are not limited to: carbamazepine, fosphenyloin, lamotrignine, lidocaine, mexiletine, oxcarbazepine, phenyloin, and combinations thereof.

Representative sympatholytics include, but are not limited to: atenolol, clonidine, doxazosin, guanethidine, guanfacine, modafinil, phentolamine, prazosin, reserpine, tolazoline (e.g., tolazoline hydrochloride), tamsulosin, and combinations thereof.

The following formulations illustrate representative pharmaceutical compositions of the present invention:

Exemplary Hard Gelatin Capsules for Oral Administration

A compound of the invention (50 g), spray-dried lactose (440 g) and magnesium stearate (10 g) are thoroughly blended. The resulting composition is then loaded into hard gelatin capsules (500 mg of composition per capsule).

Alternately, a compound of the invention (20 mg) is thoroughly blended with starch (89 mg), microcrystalline cellulose (89 mg) and magnesium stearate (2 mg). The mixture is then passed through a No. 45 mesh U.S. sieve and loaded into a hard gelatin capsule (200 mg of composition per capsule).

Exemplary Gelatin Capsule Formulation for Oral Administration

A compound of the invention (100 mg) is thoroughly blended with polyoxyethylene sorbitan monooleate (50 mg) and starch powder (250 mg). The mixture is then loaded into a gelatin capsule (400 mg of composition per capsule).

Alternately, a compound of the invention (40 mg) is thoroughly blended with microcrystalline cellulose (Avicel PH 103; 259.2 mg) and magnesium stearate (0.8 mg). The mixture is then loaded into a gelatin capsule (Size #1, White, Opaque) (300 mg of composition per capsule).

Exemplary Tablet Formulation for Oral Administration

A compound of the invention (10 mg), starch (45 mg) and microcrystalline cellulose (35 mg) are passed through a No. 20 mesh U.S. sieve and mixed thoroughly. The granules so produced are dried at 50-60° C. and passed through a No. 16 mesh U.S. sieve. A solution of polyvinylpyrrolidone (4 mg as a 10% solution in sterile water) is mixed with sodium carboxymethyl starch (4.5 mg), magnesium stearate (0.5 mg), and talc (1 mg), and this mixture is then passed through a No. 16 mesh U.S. sieve. The sodium carboxymethyl starch, magnesium stearate and talc are then added to the granules. After mixing, the mixture is compressed on a tablet machine to afford a tablet weighing 100 mg.

Alternately, a compound of the invention (250 mg) is thoroughly blended with microcrystalline cellulose (400 mg), silicon dioxide fumed (10 mg), and stearic acid (5 mg). The mixture is then compressed to form tablets (665 mg of composition per tablet).

Alternately, a compound of the invention (400 mg) is thoroughly blended with cornstarch (50 mg), croscarmellose sodium (25 mg), lactose (120 mg), and magnesium stearate (5 mg). The mixture is then compressed to form a single-scored tablet (600 mg of compositions per tablet).

Exemplary Suspension Formulation for Oral Administration

The following ingredients are mixed to form a suspension containing 100 mg of active agent per 10 mL of suspension:

Ingredients Amount Compound of the invention 1.0 g Fumaric acid 0.5 g Sodium chloride 2.0 g Methyl paraben 0.15 g Propyl paraben 0.05 g Granulated sugar 25.5 g Sorbitol (70% solution) 12.85 g Veegum ® K 1.0 g (magnesium aluminum silicate) Flavoring 0.035 mL Colorings 0.5 mg Distilled water q.s. to 100 mL

Exemplary Injectable Formulation for Administration by Injection

A compound of the invention (0.2 g) is blended with 0.4 M sodium acetate buffer solution (2.0 mL). The pH of the resulting solution is adjusted to pH 4 using 0.5 N aqueous hydrochloric acid or 0.5 N aqueous sodium hydroxide, as necessary, and then sufficient water for injection is added to provide a total volume of 20 mL. The mixture is then filtered through a sterile filter (0.22 micron) to provide a sterile solution suitable for administration by injection.

Exemplary Compositions for Administration by Inhalation

A compound of the invention (0.2 mg) is micronized and then blended with lactose (25 mg). This blended mixture is then loaded into a gelatin inhalation cartridge. The contents of the cartridge are administered using a dry powder inhaler, for example.

Alternately, a micronized compound of the invention (10 g) is dispersed in a solution prepared by dissolving lecithin (0.2 g) in demineralized water (200 mL). The resulting suspension is spray dried and then micronized to form a micronized composition comprising particles having a mean diameter less than about 1.5 μm. The micronized composition is then loaded into metered-dose inhaler cartridges containing pressurized 1,1,1,2-tetrafluoroethane in an amount sufficient to provide about 10 μg to about 500 μg of the compound of the invention per dose when administered by the inhaler.

Alternately, a compound of the invention (25 mg) is dissolved in citrate buffered (pH 5) isotonic saline (125 mL). The mixture is stirred and sonicated until the compound is dissolved. The pH of the solution is checked and adjusted, if necessary, to pH 5 by slowly adding aqueous 1N sodium hydroxide. The solution is administered using a nebulizer device that provides about 10 μg to about 500 μg of the compound of the invention per dose.

EXAMPLES

The following Preparations and Examples are provided to illustrate specific embodiments of the invention. These specific embodiments, however, are not intended to limit the scope of the invention in any way unless specifically indicated.

The following abbreviations have the following meanings unless otherwise indicated and any other abbreviations used herein and not defined have their standard meaning:

AcOH acetic acid Boc t-butoxycarbonyl BSA bovine serum albumin DCM dichloromethane (i.e., methylene chloride) DIAD diisopropyl azodicarboxylate DIPEA N, N-diisopropylethylamine DMEM Dulbecco's Modified Eagle's Medium DMSO dimethylsulfoxide EDTA ethylenediaminetetraacetic acid EtOAc ethyl acetate EtOH ethanol FBS fetal bovine serum hDAT human dopamine transporter HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid hNET human norepinephrine transporter hSERT human serotonin transporter 5-HT 5-hydroxytryptamine IPA isopropyl alcohol IPAc isopropyl acetate MeCN acetonitrile (CH₃CN) MeOH methanol NA noradrenaline PBS phosphate buffered saline PPh₃ triphenylphosphine TFA trifluoroacetic acid THF tetrahydrofuran TsCl p-toluenesulfonyl chloride or 4-methylbenzenesulfonyl chloride

Any other abbreviations used herein but not defined have their standard, generally accepted meaning Unless noted otherwise, all materials, such as reagents, starting materials and solvents, were purchased from commercial suppliers (such as Sigma-Aldrich, Fluka Riedel-de Haën, and the like) and were used without further purification.

Preparation 1 4-[2-(Toluene-4-sulfonyloxymethyl)phenyl]piperidine-1-carboxylic Acid t-Butyl Ester

4-(2-Carboxyphenyl)piperidine-1-carboxylic acid t-butyl ester (5.0 g, 16 mmol, 1.0 eq.) and THF (130 mL, 1.7 mol) were combined at room temperature under nitrogen. Borane dimethyl sulfide complex (2.9 mL, 33 mmol, 2.0 eq.) was added dropwise and the mixture was stirred for 5 minutes, then heated at reflux for 1 hour. The mixture was cooled to room temperature, and the reaction was quenched dropwise with MeOH (40 mL), then concentrated by rotary evaporation. The material was azeotroped with MeOH (2×40 mL). The mixture was then diluted with EtOAc (100 mL), and washed with 1 M HCl (2×50 mL), then NaHCO₃ (2×50 mL), then saturated aqueous NaCl (1×50 mL). The organic layer was dried over anhydrous Na₂SO₄, filtered, and concentrated in vacuo to yield 4-(2-hydroxymethylphenyl)piperidine-1-carboxylic acid t-butyl ester (4.8 g) as a clear, light yellow oil that solidified upon sitting.

¹H NMR (CDCl₃) δ (ppm) 7.34-7.22 (m, 3H); 7.19 (dt, J=1.6 Hz, 7.2, 1H); 4.73 (s, 2H); 4.32-4.14 (m, 2H); 3.00 (tt, J=4.0 Hz, 12.0, 1H); 2.80 (t, J=11.6 Hz, 2H); 1.78-1.56 (m, 4H); 1.47 (m, 9H).

4-(2-Hydroxymethylphenyl)piperidine-1-carboxylic acid t-butyl ester (0.4 g, 1.0 mmol, 1.0 eq.) and triethylenediamine (220 mg, 2.0 mmol, 1.4 eq.) were dissolved in DCM (11 mL, 170 mmol). The mixture was cooled at 0° C. under nitrogen, TsCl (290 mg, 1.5 mmol, 1.1 eq.) was added, and the mixture was stirred at 0° C. for an additional 60 minutes. The mixture was diluted with EtOAc (50 mL) and washed with water (2×25 mL). The organic layer was dried over anhydrous Na₂SO₄, filtered and concentrated by rotary evaporation to yield the title compound (500 mg), which was used without further purification.

¹H NMR (CDCl₃) δ (ppm) 7.81 (t, J=2.0 Hz, 1H); 7.79 (t, J=2.0 Hz, 1H); 7.37-7.32 (m, 4H); 7.25-7.21 (m, 1H); 7.21-7.13 (m, 1H), 5.12 (s, 2H); 4.34-4.12 (m, 2H); 2.81-2.61 (m, 3H); 2.45 (s, 3H); 1.70-1.52 (m, 4H); 1.48 (s, 9H).

Preparation 2 4-(2-Methanesulfonyloxymethylphenyl)piperidine-1-carboxylic Acid t-Butyl Ester

4-(2-Carboxyphenyl)piperidine-1-carboxylic acid t-butyl ester (5.0 g, 160 mmol, 1.0 eq.) and THF (100 mL, 1.0 mol) were combined at room temperature under nitrogen. 1.0M Borane-THF complex in THF (32.7 mL, 32.7 mmol, 2.0 eq.) was added dropwise over 10 minutes (5° C. exotherm, gas evolution). The mixture was stirred at room temperature for 5 minutes, then heated at 50° C. for 1 hour. The mixture was cooled to room temperature, and the reaction was quenched slowly with MeOH (30 mL) (mild exotherm, significant gas evolution), then concentrated by rotary evaporation. The material was azeotroped with MeOH (2×50 mL). The crude product was dissolved in EtOAc (100 mL, 1 mol), washed with NaHCO₃ (50 mL), then saturated aqueous NaCl (50 mL). The organic layer was dried over anhydrous Na₂SO₄, filtered, and concentrated in vacuo to yield 4-(2-hydroxymethylphenyl)piperidine-1-carboxylic acid t-butyl ester (4.4 g) as a clear, light yellow oil that solidified upon sitting.

4-(2-Hydroxymethylphenyl)piperidine-1-carboxylic acid t-butyl ester (50.0 g, 172 mmol, 1.0 eq.) was dissolved in DCM (500 mL, 8000 mmol). The mixture was cooled at 0° C. under nitrogen and methanesulfonic anhydride (44.8 g, 257 mmol, 1.5 eq.) was added in one portion. DIPEA (47.8 mL, 274 mmol, 1.6 eq.) was added dropwise over 5 minutes and the mixture was stirred at 0° C. for 90 minutes. Water (400 mL, 20 mol) was added and the mixture was stirred for 5 minutes. The phases were separated, and the organic layer was washed with water (300 mL), dried over Na₂SO₄, and the solvent removed to yield the title compound (70 g) as a thick oil, which was used without further purification.

¹H NMR (400 MHz, DMSO-d₆) δ (ppm) 7.37-7.43 (m, 3H), 7.31 (d, 1H), 7.22 (m, 2H), 5.38 (s, 2H), 4.28 (m, 2H), 2.92-3.10 (m, 1H), 2.92 (s, 3H), 2.80-2.92 (m, 2H), 1.63-1.81 (m, 4H), 1.51 (s, 9H).

Example 1 4-[2-(2,4,6-Trifluorophenoxymethyl)phenyl]piperidine

4-[2-(Toluene-4-sulfonyloxymethyl)phenyl]piperidine-1-carboxylic acid t-butyl ester (2.1 g, 4.7 mmol, 1.0 eq.) was dissolved in MeCN (46 mL, 890 mmol) and added to K₂CO₃ (1.9 g, 14 mmol, 3.0 eq.) and 2,4,6-trifluorophenol (1.0 g, 7.0 mmol, 1.5 eq.). The mixture was shaken at 50° C. overnight, then cooled to room temperature. The supernatant was separated from the K₂CO₃ and other solids. TFA (7 mL, 90 mmol, 20.0 eq.) was added to the supernatant and the mixture was shaken overnight at room temperature. The solution was then concentrated to yield a crude residue. The residue was dissolved in 5.0 mL 1:1 AcOH/H₂O, then in an additional 2.0 mL AcOH, filtered and purified by preparative HPLC to yield the title compound as a TFA salt (1.3 g, 97.5% purity). MS m/z: [M+H]⁺ calcd for C₁₈H₁₈F₃NO, 322.13. found 322.2.

¹H NMR (CDCl₃) δ (ppm) 9.83 (br.s, 1H); 9.32 (br.s, 1H); 7.46-7.39 (m, 2H); 7.32 (d, J=6.8 Hz, 1H); 7.26-7.21 (m, 1H); 6.76-6.66 (m, 2H); 5.07 (s, 2H); 3.69-3.50 (m, 2H); 3.38 (t, J=11.6 Hz, 1H); 3.20-3.02 (m, 2H); 2.19 (q, J=12.8 Hz, 2H); 2.12-2.01 (m, 2H).

Synthesis of 4-[2-(2,4,6-Trifluorophenoxymethyl)phenyl]piperidine as a Crystalline HCl Salt

4-(2-Methanesulfonyloxymethylphenyl)piperidine-1-carboxylic acid t-butyl ester (27.0 g, 60.6 mmol, 1.0 eq.) was dissolved in MeCN (540 mL) and added to K₂CO₃ (25 g, 180 mmol, 3.0 eq.) and 2,4,6-trifluorophenol (13.5 g, 90.9 mmol, 1.5 eq.). The mixture was vigorously stirred at 50° C. for 6 hours, removed from the heat, and stirred overnight. The mixture was cooled at room temperature, and diluted with EtOAc (700 mL) and water (700 mL). The phases were separated, and the organic layer was washed twice with 1.0 M NaOH in water (2×400 mL) and saturated aqueous NaCl (1×400 mL), then dried over Na₂SO₄ and the solvent removed to yield crude 4-[2-(2,4,6-trifluorophenoxymethyl)-phenyl]piperidine-1-carboxylic acid t-butyl ester (25.0 g). The crude product was combined with smaller scale runs for a total of 30 g, and purified by chromatography (0-10% EtOAc in hexanes) to yield 4-[2-(2,4,6-trifluorophenoxymethyl)phenyl]piperidine-1-carboxylic acid t-butyl ester (22.0 g).

The t-butyl ester (22.0 g, 31.3 mmol, 1.0 eq.) was combined with 1.25M HCl in EtOH (250 mL, 310 mmol, 10.0 eq.). The mixture was stirred at room temperature for 8 hours, then stored at −10° C. over approximately 48 hours. Most of solvent was removed by rotary evaporation. To the resulting thick slurry was added EtOAc (80 mL), followed by stirring at room temperature for 2 hours. First crop was isolated by filtration, and the filter cake was washed with EtOAc (20 mL) and dried to yield the title compound as a hydrochloride salt (8.5 g, >99% purity) white solid. HPLC of the filtrate shows ˜25% area of product. For the second crop, the solvent was removed by rotary evaporation and the resulting solid (˜10 g) was slurried in EtOAc (40 mL), first at room temperature, then at 60° C., and again at room temperature to yield the title compound as a hydrochloride salt (1.7 g, >99% purity).

Two lots of the hydrochloride salt (18.5 g, 51.7 mmol) were combined with EtOAc (75 mL, 770 mmol). The resulting thick but free-flowing slurry was heated at 65° C. for 30 minutes, cooled to room temperature, and filtered. The flask and the filter cake were washed with EtOAc (20 mL), and the solids dried under high vacuum at room temperature overnight to yield the crystalline hydrochloride salt (18.2 g, 99.3% purity).

Good crystallinity was observed by XRPD. LC-MS (2 mg in 2 mL of 1:1 MeCN:1M aq HCl; API 150EX LC/MS System) was found to be consistent with structure. NMR (DMSO-d₆, Varian VnmrJ 400) was found to be consistent with the structure and the salt form.

Alternate Synthesis of 4-[2-(2,4,6-Trifluorophenoxymethyl)phenyl]piperidine as a Crystalline HCl Salt

Acetyl chloride (83.5 mL, 1170 mmol) was slowly added to EtOH (140 mL, 2.4 mol). 4-[2-(2,4,6-Trifluorophenoxymethyl)phenyl]piperidine-1-carboxylic acid t-butyl ester (55.0 g, 117 mmol) dissolved in EtOH (100 mL, 2.0 mol) was added and the resulting mixture was stirred at room temperature for 6 hours. Most of solvent was removed by rotary evaporation. To the resulting thick slurry was added EtOAc (300 mL), followed by partial solvent removal to ˜100 mL. Fresh EtOAc (200 mL) was added and the resulting slurry was stirred for 1 hour, filtered and dried to yield a hydrochloride salt (28.0 g, ˜99% purity). The filtrate was concentrated to a thick paste and IPAc (100 mL) was added, stirred for 1 hour, filtered and dried to further yield 5.0 g of the hydrochloride salt (˜99% purity).

Two lots of the hydrochloride salt (83.0 g, 230 mmol, ˜99% purity) were combined with EtOAc (250 mL, 2.6 mol). The resulting slurry was heated at 70° C. and then slowly cooled to room temperature, followed by stirring overnight. The resulting free-flowing slurry was filtered and the filter cake was washed with EtOAc (50 mL) then dried under high vacuum for approximately 48 hours to yield a crystalline hydrochloride salt (81.0 g, >99% purity). ¹H NMR (DMSO-d₆, 400 Hz) was found to be consistent with the structure and the salt form of Example 1.

The crystalline hydrochloride salt (50.0 g, 1.40 mol, >99% purity) was dissolved in IPA (250 mL, 3.3 mol), and the resulting slurry was heated to 75° C. Water (25 mL, 1.4 mol) was added. Complete dissolution was observed in 5 minutes, and the internal temperature of the solution was 65° C. The solution was slowly cooled to room temperature and then stirred at room temperature overnight. The resulting solids were filtered and dried under air for 2 hours to yield a semi-dry product. The solids were then dried under high vacuum at room temperature for approximately 48 hours to yield the title crystalline hydrochloride salt (44.1 g, 99.5% purity). The material exhibited good crystallinity by XRPD and DSC.

The title crystalline hydrochloride salt (151.1 g, 99.5% purity) was also prepared in a similar manner using 175.0 g of the hydrochloride salt and 10 volumes of 5% water in IPA (total of 90 mL water and 1.8 L IPA).

Example 2 4-[2-(2,6-Difluorophenoxymethyl)phenyl]piperidine

4-[2-(Toluene-4-sulfonyloxymethyl)phenyl]piperidine-1-carboxylic acid t-butyl ester (225 mg, 505 μmol, 1.0 eq.) was dissolved in MeCN (5.0 mL, 97 mmol) and added to K₂CO₃ (210 mg, 1.5 mmol, 3.0 eq.) and 2,6-difluorophenol (98 mg, 760 μmol, 1.5 eq.). The mixture was shaken at 50° C. overnight, then cooled to room temperature. The supernatant was separated from the K₂CO₃ and other solids.

TFA (800 μL, 10 mmol, 20.0 eq.) was added to the supernatant and the mixture was shaken overnight at room temperature. The solution was then concentrated to yield a crude residue. The residue was dissolved in 1.5 mL 1:1 AcOH/H₂O, then in an additional 0.3 mL AcOH, filtered and purified by preparative HPLC to yield the title compound as a TFA salt (115 mg, 95% purity). MS m/z: [M+H]⁺ calcd for C₁₈H₁₉F₂NO, 304.14. found 304.2.

The following NMR data was obtained for a separate lot of material that was prepared in a manner similar to that described above:

¹H NMR (CDCl₃) δ (ppm) 9.60 (br.s, 1H); 9.25 (br.s, 1H); 7.42-7.37 (m, 2H); 7.33 (d, J=7.6 Hz, 1H); 7.26-7.20 (m, 1H); 7.03-6.86 (m, 3H); 5.11 (s, 2H); 3.64-3.50 (m, 2H); 3.38 (t, J=11.0 Hz, 1H); 3.16-3.00 (m, 2H); 2.18 (q, J=12.4 Hz, 2H); 2.10-2.01 (m, 2H).

Example 3

Following the procedures described in the examples above, and substituting the appropriate starting materials and reagents, compounds 3-1 to 3-10, having formula Ia, were also prepared:

(Ia)

MS m/z: [M + H]⁺ Cmpd R³ R⁴ R⁵ R⁶ Formula calcd found 3-1 H H H H C₁₈H₂₀FNO 286.15 286.2 3-2 H Cl H F C₁₈H₁₈ClF₂NO 338.10 338.0 3-3 F H H F C₁₈H₁₈F₃NO 322.13 322.2 3-4 Cl H H F C₁₈H₁₈ClF₂NO 338.10 338.0 3-5 —CH₃ H H F C₁₉H₂₁F₂NO 318.16 318.2 3-6 H H F Cl C₁₈H₁₈ClF₂NO 338.10 338.0 3-7 H H H Cl C₁₈H₁₉ClFNO 320.11 320.0 3-8 H H H Br C₁₈H₁₉BrFNO 364.06 364.0 3-9 H Br H Cl C₁₈H₁₈BrClFNO 398.02 398.0 3-10 H F H Cl C₁₈H₁₈ClF₂NO 338.10 338.0

Preparation 3 4-(4,4,5,5-Tetramethyl-[1,3,2]dioxaborolan-2-yl)-3,6-dihydro-2H-pyridine-1-carboxylic Acid t-Butyl Ester

Boc-4-piperidone (1.99 g, 10 mmol) was dissolved in THF (10 mL, 0.2 mol) and was cooled at −20° C. 1.0 M of sodium bis(trimethylsilyl)amide in THF (11.0 mL, 11 mmol) was slowly added. The mixture was stirred at −30° C. to −20° C. for 30 minutes. N-Phenyl-bis(trifluoromethanesulfonimide) (3.57 g, 10 mmol) was added in THF (7 mL). The resulting mixture was stirred at −20° C. to −10° C. for 60 minutes, then 1.0 M NaOH in water (9.4 mL, 9.4 mmol) was added. The mixture was allowed to warm to room temperature. EtOAc (60.0 mL) and heptane (30 mL) were added to the mixture and stirred for 5 minutes. The layers were separated and the organic layer was washed with 1N NaOH (5×25 mL), saturated aqueous NaCl (10.0 mL), dried over Na₂SO₄, filtered and concentrated to yield 4-trifluoromethanesulfonyloxy-3,6-dihydro-2H-pyridine-1-carboxylic acid t-butyl ester (3.1 g) as a yellowish oil, which was used without further purification.

¹H NMR (CDCl₃) δ (ppm) 5.76 (m, 1H); 4.04 (m, 2H); 3.62 (m, 2H); 2.45 (m, 2H); 1.48 (s, 9H).

4-Trifluoromethanesulfonyloxy-3,6-dihydro-2H-pyridine-1-carboxylic acid t-butyl ester (990 mg, 3.0 mmol) was dissolved in 1,4-dioxane (9 mL, 100 mmol) and potassium acetate (883.3 mg, 9.0 mmol), bis(pinacolato)diboron (788 mg, 3.1 mmol), 1,1′-bis(diphenylphosphino)ferrocene-palladium(II)dichloride dichloromethane complex (52 mg, 63 μmol), and 1,1′-bis(diphenylphosphino)ferrocene (38 mg, 68 μmol) were added. The mixture was degassed and purged with nitrogen (4×), followed by heating at 80° C. for 17 hours. The mixture was allowed to cool to room temperature and filtered through Celite® using EtOAc (25 mL) to wash the product, yielding the title compound (296 mg) as a semi-waxy white solid.

Preparation 4 4-(4-Fluoro-2-hydroxymethylphenyl)piperidine-1-carboxylic Acid t-Butyl Ester

Methyl 2-bromo-5-fluorobenzoate (1.8 g, 7.5 mmol), 4-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-3,6-dihydro-2H-pyridine-1-carboxylic acid t-butyl ester (2.3 g, 7.5 mmol), THF (69 mL, 850 mmol) and 2 M of sodium carbonate in water (15.0 mL, 30.0 mmol) were combined, and the mixture was degassed and flushed with nitrogen. Bis(triphenylphosphine)palladium(II) chloride (158 mg, 225 μmol) was added, and the mixture was again degassed and flushed with nitrogen. The mixture was heated at 80° C. for 1 hour. The mixture was then cooled and the layers separated, diluted with EtOAc (50 mL), washed with saturated aqueous NaCl (30 mL), dried over Na₂SO₄, filtered and concentrated in vacuo. The crude product was purified by flash chromatography (0-50% EtOAc in hexanes). A solution of the crude material and Pearlman's Catalyst (0.1:0.4, Palladium hydroxide:carbon black, 1.1 g, 1.5 mmol) in MeOH (60.8 mL, 150 mmol) was hydrogenated at 1 atm at room temperature overnight. The mixture was then evacuated, purged with nitrogen, filtered through Celite® and concentrated to yield a colorless oil. This oil was dissolved in THF (30 mL, 400 mmol) and treated with borane-dimethyl sulfide complex (1.3 mL, 15.0 mmol) at room temperature. The mixture was heated to reflux for 5 hours. After cooling to room temperature, MeOH (20 mL) was slowly added and removed by rotary evaporation. Another 20 mL of MeOH was added and removed by rotary evaporation. The residue was then dissolved in EtOAc (100 mL) and washed with 1N HCl and sat. NaHCO₃, dried over Na₂SO₄, filtered and concentrated. The material was then purified by silica gel chromatography (0-50% EtOAc in hexanes) to yield the title compound (924 mg) as a colorless sticky solid.

¹H NMR (CDCl₃) δ (ppm) 7.21 (br.s, 1H); 7.16 (m, 1H); 6.98 (m, 1H); 4.76 (br.s, 2H); 4.24 (m, 2H); 2.89 (m, 1H); 2.80 (m, 2H); 1.72 (m, 2H); 1.60 (m, 2H); 1.47 (s, 9H).

Example 4 4-[4-Fluoro-2-(2,4,6-trifluorophenoxymethyl)phenyl]piperidine

DIAD (23.6 μL, 120 μmol) was added to a solution of PPh₃ (28.9 mg, 110 μmol) in toluene (533 μL, 5 mmol). The mixture was stirred briefly, and 4-(4-fluoro-2-hydroxymethylphenyl)piperidine-1-carboxylic acid t-butyl ester (30.9 mg, 100 μmol) was added. This mixture was combined with 2,4,6-trifluorophenol (14.8 mg), heated at 80° C. for 4 hours, then concentrated. The crude material was deprotected using 1.25 M HCl in EtOH (1 mL) overnight at room temperature. The material was then concentrated and the residue was purified by preparative HPLC to yield the title compound as a TFA salt (7.8 mg, 100% purity). MS m/z: [M+H]⁺ calcd for C₁₈H₁₇F₄NO, 340.12. found 340.0.

Example 5

Following the procedures described in the examples above, and substituting the appropriate starting materials and reagents, compounds 5-1 to 5-17, having formula Ib, were also prepared:

(Ib)

MS m/z: [M + H]⁺ Cmpd R¹ R³ R⁴ R⁵ R⁶ Formula calcd found 5-1 5-fluoro H H H H C₁₈H₁₉F₂NO 304.14 304.2 5-2 4-fluoro H H H F C₁₈H₁₈F₃NO 322.13 322.0 5-3 5-fluoro H H H F C₁₈H₁₈F₃NO 322.13 322.2 5-4 6-fluoro H F H F C₁₈H₁₇F₄NO 340.12 340.0 5-5 5-fluoro H F H F C₁₈H₁₇F₄NO 340.12 340.0 5-6 3-fluoro F H H F C₁₈H₁₇F₄NO 340.12 340.0 5-7 5-fluoro F H H F C₁₈H₁₇F₄NO 340.12 340.0 5-8 5-fluoro H H F Cl C₁₈H₁₇ClF₃NO 356.10 356.0 5-9 4-fluoro H H H Cl C₁₈H₁₈ClF₂NO 338.10 338.0 5-10 6-fluoro H H H Cl C₁₈H₁₈ClF₂NO 338.10 338.0 5-11 6-fluoro H H H H C₁₈H₁₉F₂NO 304.14 304.2 5-12 6-fluoro H H H F C₁₈H₁₈F₃NO 322.13 322.2 5-13 5-CF₃ H H H Cl C₁₉H₁₈ClF₄NO 388.10 388.0 5-14 5-CF₃ F H H F C₁₉H₁₇F₆NO 390.12 390.0 5-15 6-fluoro F H H F C₁₈H₁₇F₄NO 340.12 340.0 5-16 5-CF₃ H F H F C₁₉H₁₇F₆NO 390.12 390.0 5-17 6-fluoro H H F Cl C₁₈H₁₇ClF₃NO 356.10 356.0

Example 6

Following the procedures described in the examples above, and substituting the appropriate starting materials and reagents, compounds 6-1 to 6-7, having formula II-3, were also prepared:

(Ic)

MS m/z: [M + H]⁺ Cmpd R¹ R³ R⁴ R⁵ R⁶ Formula calcd found 6-1 4,5-difluoro H H H F C₁₈H₁₇F₄NO 340.12 340.0 6-2 4,5-difluoro H F H F C₁₈H₁₆F₅NO 358.12 358.0 6-3 4,5-difluoro H H H Cl C₁₈H₁₇ClF₃NO 356.10 356.0 6-4 4,6-difluoro H H H F C₁₈H₁₇F₄NO 340.12 340.0 6-5 4,6-difluoro F H H F C₁₈H₁₆F₅NO 358.12 358.0 6-6 4,6-difluoro H F H F C₁₈H₁₆F₅NO 358.12 358.3 6-7 5,6-difluoro H F H F C₁₈H₁₆F₅NO 358.12 358.2 6-8 4,6-difluoro H H F Cl C₁₈H₁₆ClF₄NO 374.09 374.0

Assay 1 hSERT, hNET, and hDAT Binding Assays

Membrane radioligand binding assays were used to measure competitive inhibition of labeled ligand (³H-citalopram or ³H-nisoxetine or ³H-WIN35428) binding to membranes prepared from cells expressing the respective human recombinant transporter (hSERT or hNET or hDAT) in order to determine the pK_(i) values of test compounds at the transporters.

Membrane Preparation from Cells Expressing hSERT, hNET, or hDAT

Recombinant human embryonic kidney (HEK-293) derived cell lines stably transfected with hSERT or hNET, respectively, were grown in DMEM medium supplemented with 10% dialyzed FBS (for hSERT) or FBS (for hNET), 100 μg/ml penicillin, 100 μg/ml streptomycin, 2 mM L-glutamine and 250 μg/ml of the aminoglycoside antibiotic G418, in a 5% CO₂ humidified incubator at 37° C. When cultures reached 80% confluence, the cells were washed thoroughly in PBS (without Ca²⁺ and Mg²⁺) and lifted with 5 mM EDTA in PBS. Cells were pelleted by centrifugation, resuspended in lysis buffer (10 mM Tris-HCl, pH7.5 containing 1 mM EDTA), homogenized, pelleted by centrifugation, then resuspended in 50 mM Tris-HCl, pH 7.5 and 10% sucrose at 4° C. Protein concentration of the membrane suspension was determined using a Bio-Rad Bradford Protein Assay kit. Membranes were snap frozen and stored at −80° C. Chinese hamster ovary membranes expressing hDAT (CHO-DAT) were purchased from PerkinElmer and stored at −80° C.

Binding Assays

Binding assays were performed in a 96-well assay plate in a total volume of 200 μl assay buffer (50 mM Tris-HCl, 120 mM NaCl, 5 mM KCl, pH 7.4) with 0.5, 1, and 3 μg membrane protein, for SERT, NET and DAT, respectively. Saturation binding studies, to determine radioligand K_(d) values for ³H-citalopram, ³H-nisoxetine, or ³H-WIN35428, respectively were conducted using 12 different radioligand concentrations ranging from 0.005-10 nM (³H-citalopram); 0.01-20 nM (³H-nisoxetine) and 0.2-50 nM (³H-WIN35428). Displacement assays for determination of pK_(i) values of test compounds were conducted with 1.0 nM ³H-citalopram, 1.0 nM ³H-nisoxetine or 3.0 nM ³H-WIN35428, at 11 different concentrations of test compound ranging from 10 μM to 100 μm.

Stock solutions (10 mM in DMSO) of test compound were prepared and serial dilutions made using Dilution Buffer (50 mM Tris-HCl, 120 mM NaCl, 5 mM KCl, pH 7.4, 0.1% BSA, 400 μM ascorbic acid). Non-specific radioligand binding was determined in the presence of 1 μM duloxetine, 1 μM desipramine or 10 μM GBR12909 (each in Dilution Buffer) for the hSERT, hNET or hDAT assays, respectively.

Following a 60 minute incubation at 22° C. (or a period sufficient to reach equilibrium), the membranes were harvested by rapid filtration over a 96-well UniFilter GF/B plate, pretreated with 0.3% polyethyleneimine, and washed 6 times with 300 μl wash buffer (50 mM Tris-HCl, 0.9% NaCl, pH 7.5 at 4° C.). Plates were dried overnight at room temperature, ˜45 μl of MicroScint™-20 (Perkin Elmer) added and bound radioactivity quantitated via liquid scintillation spectroscopy. Competitive inhibition curves and saturation isotherms were analyzed using GraphPad Prism Software package (GraphPad Software, Inc., San Diego, Calif.). IC₅₀ values were generated from concentration response curves using the Sigmoidal Dose Response (variable slope) algorithm in Prism GraphPad. K_(d) and B_(max) values for the radioligand were generated from saturation isotherms using the Saturation Binding Global Fit algorithm in Prism GraphPad. pK_(i) (negative decadic logarithm of K_(i)) values for test compounds were calculated from the best-fit IC₅₀ values, and the K_(d) value of the radioligand, using the Cheng-Prusoff equation (Cheng & Prusoff (1973) Biochem. Pharmacol. 22(23):3099-3108): K_(i)=IC₅₀/(1+[L]/K_(d)), where [L]=concentration radioligand.

All the aforementioned compounds were tested in this assay and found to exhibit a SERT pK_(i)≧7.9 and a NET pK_(i)≧8.0.

Assay 2 hSERT, hNET, and hDAT Neurotransmitter Uptake Assays

Neurotransmitter uptake assays were used to measure competitive inhibition of ³H-serotonin (³H-5-HT), ³H-norepinephrine (³H-NE), and ³H-dopamine (³H-DA) uptake into cells expressing the respective transporter (hSERT, hNET or hDAT) in order to determine the pIC₅₀ values of test compounds at the transporters.

³H-5-HT, ³H-NE, and ³H-DA Uptake Assays

HEK-293 derived cell lines stably-transfected with hSERT, hNET, or hDAT, respectively, were grown in DMEM medium supplemented with 10% dialyzed FBS (for hSERT) or FBS (for hNET and hDAT), 100 μg/ml penicillin, 100 μg/ml streptomycin, 2 mM L-glutamine and 250 μg/ml of the aminoglycoside antibiotic G418 (for hSERT and hNET) or 800 ug/ml (for hDAT), in a 5% CO₂ humidified incubator at 37° C. When cultures reached 80% confluence, the cells were washed thoroughly in PBS (without Ca²⁺ and Mg²⁺) and lifted with 5 mM EDTA in PBS. Cells were harvested by centrifugation at 1100 rpm for 5 minutes, washed once by resuspension in PBS, then centrifuged. The supernatant was discarded and the cell pellet resuspended, by gentle trituration, in room temperature Krebs-Ringer bicarbonate buffer containing HEPES (10 mM), CaCl₂ (2.2 mM), ascorbic acid (200 μM) and pargyline (200 μM), pH 7.4. The final concentration of cells in the cell suspension was 7.5×10⁴ cells/ml, 1.25×10⁵ cells/ml, and 5.0×10⁴ cells/ml for SERT, NET, and DAT cell lines, respectively.

Neurotransmitter uptake assays were performed in a 96-well assay plate in a total volume of 400 μL, assay buffer (Krebs-Ringer bicarbonate buffer containing HEPES (10 mM), CaCl₂ (2.2 mM), ascorbic acid (200 μM) and pargyline (200 μM), pH 7.4) with 1.5×10⁴ and 2.5×10⁴ cells, for SERT and NET, respectively. Competition assays for determination of pIC₅₀ values of test compounds were conducted with 11 different concentrations, ranging from 10 μM to 100 μM. Stock solutions (10 mM in DMSO) of test compound were prepared and serial dilutions prepared using 50 mM Tris-HCl, 120 mM NaCl, 5 mM KCl, pH 7.4, 0.1% BSA, 400 μM ascorbic acid. Test compounds were incubated for 30 minutes at 37° C. with the respective cells, prior to addition of radiolabeled neurotransmitter, ³H-5-HT (20 nM final concentration), ³H-NE (50 nM final concentration), or ³H-DA (100 nM final concentration). Non-specific neurotransmitter uptake was determined in the presence of 2.5 μM duloxetine or 2.5 μM desipramine (each in Dilution Buffer) for the hSERT, hNET, or hDAT assays, respectively.

Following a 10 minute incubation, at 37° C., with radioligand, the cells were harvested by rapid filtration over a 96-well UniFilter GF/B plate, pretreated with 1% BSA, and washed 6 times with 650 μl wash buffer (ice cold PBS). Plates were dried overnight at 37° C., ˜45 μl of MicroScint™-20 (Perkin Elmer) added and incorporated radioactivity quantitated via liquid scintillation spectroscopy. Competitive inhibition curves were analyzed using GraphPad Prism Software package (GraphPad Software, Inc., San Diego, Calif.). IC₅₀ values were generated from concentration response curves using the Sigmoidal Dose Response (variable slope) algorithm in Prism GraphPad.

Assay 3 Ex Vivo SERT and NET Transporter Occupancy Studies

Ex vivo radioligand binding and neurotransmitter uptake assays were used to determine the in vivo occupancy of SERT and NET, in selected brain regions, following in vivo administration (acute or chronic) of test compounds. Following administration of test compound (by intravenous, intraperitoneal, oral, subcutaneous or other route) at the appropriate dose (0.0001 to 100 mg/kg), rats (≧n=4 per group) were euthanized at specific time points (10 minutes to 48 hours) by decapitation and the brain dissected on ice. Relevant brain regions were dissected, frozen and stored at −80° C. until use.

Ex Vivo SERT and NET Radioligand Binding Assays

For ex vivo radioligand binding assays, the initial rates of association of SERT (³H-citalopram), and NET-(³H-nisoxetine) selective radioligands with rat brain crude homogenates, prepared from vehicle and test compound-treated animals, were monitored (see Hess et al. (2004) J. Pharmacol. Exp. Ther. 310(2):488-497). Crude brain tissue homogenates were prepared by homogenizing frozen tissue pieces in 0.15 mL (per mg wet weight) of 50 mM Tris-HCl, 120 mM NaCl, 5 mM KCl, pH 7.4 buffer. Radioligand association assays were performed in a 96-well assay plate in a total volume of 200 μl assay buffer (50 mM Tris-HCl, 120 mM NaCl, 5 mM KCl, 0.025% BSA, pH 7.4) with 650 μg wet weight tissue (equivalent to 25 μg protein). Homogenates were incubated for up to 5 minutes with ³H-citalopram (3 nM) and ³H-nisoxetine (5 nM), respectively, prior to termination of the assay by rapid filtration over a 96-well UniFilter GF/B plate, pretreated with 0.3% polyethyleneimine. Filters then were washed 6 times with 300 μl wash buffer (50 mM Tris-HCl, 0.9% NaCl, pH 7.4 at 4° C.). Non-specific radioligand binding was determined in the presence of 1 μM duloxetine, or 1 μM despiramine, for ³H-citalopram or ³H-nisoxetine, respectively. The plates were dried overnight at room temperature, ˜45 μl of MicroScint™-20 (Perkin Elmer) added and bound radioactivity quantitated via liquid scintillation spectroscopy. The initial rates of association of ³H-citalopram and ³H-nisoxetine were determined by linear regression using GraphPad Prism Software package (GraphPad Software, Inc., San Diego, Calif.). The average rate of radioligand association to brain tissue homogenates from vehicle-treated animals was determined. The % occupancy of test compounds then was determined using the following equation: % occupancy=100×(1−(initial rate association for test compound-treated tissue/mean rate association for vehicle-treated tissue)) ED₅₀ values were determined by plotting the log 10 of the dose of the test compound against the % occupancy. ED₅₀ values were generated from concentration response curves using the Sigmoidal Dose Response (variable slope) algorithm in GraphPad Prism.

Ex Vivo SERT and NET Uptake Assays

Ex vivo neurotransmitter uptake assays, in which the uptake of ³H-5-HT or ³H-NE into rat brain crude homogenates, prepared from vehicle and test compound-treated animals, were used to measure in vivo SERT and NET transporter occupancy (see Wong et al. (1993) Neuropsychopharmacology 8(1):23-33). Crude brain tissue homogenates were prepared by homogenizing frozen tissue pieces in 0.5 mL (per mg wet weight) of 10 mM HEPES buffer pH 7.4, containing 0.32 M sucrose, 200 μM ascorbic acid and 200 μM pargyline, at 22° C. Neurotransmitter uptake assays were performed in a 96-well Axygen plate in a total volume of 350 μl assay buffer (Krebs-Ringer bicarbonate buffer with 10 mM HEPES, 2.2 mM CaCl₂, 200 μM ascorbic acid and 200 μM pargyline, pH 7.4) with 50 μg protein. Homogenates were incubated for 5 minutes at 37° C. with ³H-5-HT (20 nM) and ³H-NE (50 nM), respectively, prior to termination of the assay by rapid filtration over a 96-well UniFilter GF/B plate, pretreated with 1% BSA. Plates were washed 6 times with 650 μl wash buffer (ice cold PBS) and dried overnight at 37° C., prior to addition of ˜45 μl of MicroScint™-20 (Perkin Elmer) added. Incorporated radioactivity was quantitated via liquid scintillation spectroscopy. Non-specific neurotransmitter uptake was determined in parallel assays in which tissue homogenates were incubated with ³H-5-HT (20 nM) or ³H-NE (50 nM) for 5 minutes at 4° C.

Assay 4 Other Assays

Other assays that were used to evaluate the pharmacological properties of test compounds include, but are not limited to, cold ligand binding kinetics assays (Motulsky and Mahan (1984) Molecular Pharmacol. 25(1):1-9) with membranes prepared from cells expressing hSERT or hNET; conventional membrane radioligand binding assays using radiolabeled, for example, tritiated, test compound; radioligand binding assays using native tissue from, for example rodent or human brain; neurotransmitter uptake assays using human or rodent platelets; neurotransmitter uptake assays using crude, or pure, synaptosome preparations from rodent brain.

Assay 5 Formalin Paw Test

Compounds are assessed for their ability to inhibit the behavioral response evoked by a 50 μl injection of formalin (5%). A metal band is affixed to the left hind paw of male Sprague-Dawley rats (200-250 g) and each rat is conditioned to the band for 60 minutes within a plastic cylinder (15 cm diameter). Compounds are prepared in pharmaceutically acceptable vehicles and administered systemically (i.p., p.o.) at pre-designated times before formalin challenge. Spontaneous nociceptive behaviors consisting of flinching of the injected (banded) hind paw are counted continuously for 60 minutes using an automated nociception analyzer (UCSD Anesthesiology Research, San Diego, Calif.). Antinociceptive properties of test articles are determined by comparing the number of flinches in the vehicle and compound-treated rats (Yaksh et al., “An automated flinch detecting system for use in the formalin nociceptive bioassay” (2001) J. Appl. Physiol. 90(6):2386-2402).

Assay 6 Spinal Nerve Ligation Model

Compounds are assessed for their ability to reverse tactile allodynia (increased sensitivity to an innocuous mechanical stimulus) induced by nerve injury. Male Sprague-Dawley rats are surgically prepared as described in Kim and Chung “An experimental model for peripheral neuropathy produced by segmental spinal nerve ligation in the rat” (1992) Pain 50(3):355-363. Mechanical sensitivity is determined as the 50% withdrawal response to innocuous mechanical stimuli (Chaplan et al., “Quantitative assessment of tactile allodynia in the rat paw” (1994) J. Neurosci. Methods 53(1):55-63) before and after nerve injury. One to four weeks post-surgery, compounds are prepared in pharmaceutically acceptable vehicles and administered systemically (i.p., p.o.). The degree of nerve injury-induced mechanical sensitivity before and after treatment serves as an index of the compounds' antinociceptive properties.

While the present invention has been described with reference to specific aspects or embodiments thereof, it will be understood by those of ordinary skilled in the art that various changes can be made or equivalents can be substituted without departing from the true spirit and scope of the invention. Additionally, to the extent permitted by applicable patent statues and regulations, all publications, patents and patent applications cited herein are hereby incorporated by reference in their entirety to the same extent as if each document had been individually incorporated by reference herein. 

1. A compound of formula I:

where: a is 0, 1, 2, 3, or 4; each R¹ is independently halo or trifluoromethyl; R³ is hydrogen, halo, or —C₁₋₆alkyl; R⁴, R⁵, and R⁶ are independently hydrogen or halo; or a pharmaceutically acceptable salt thereof.
 2. The compound of claim 1, where R³ is hydrogen, fluoro, chloro, or methyl.
 3. The compound of claim 1, where R⁴ is hydrogen, fluoro, chloro, or bromo.
 4. The compound of claim 1, where R⁵ is hydrogen or fluoro.
 5. The compound of claim 1, where R⁶ is hydrogen, fluoro, chloro, or bromo.
 6. The compound of claim 1, where a is
 0. 7. The compound of claim 6, where R³ is hydrogen, fluoro, chloro, or methyl; R⁴ is hydrogen, fluoro, chloro, or bromo; R⁵ is hydrogen or fluoro; and R⁶ is hydrogen, fluoro, chloro, or bromo.
 8. The compound of claim 1, where a is 0, R³ and R⁵ are hydrogen, and R⁴ and R⁶ are fluoro.
 9. The compound of claim 1, where a is
 1. 10. The compound of claim 9, where R¹ is 3-fluoro, 4-fluoro, 5-fluoro, 5-trifluoromethyl, or 6-fluoro.
 11. The compound of claim 9, where R³ is hydrogen or fluoro; R⁴ is hydrogen or fluoro; R⁵ is hydrogen or fluoro; and R⁶ is hydrogen, fluoro or chloro.
 12. The compound of claim 1, where a is
 2. 13. The compound of claim 12, where R¹ is 4,5-difluoro, 4,6-difluoro, or 5,6-difluoro.
 14. The compound of claim 12, where R³ is hydrogen or fluoro; R⁴ is hydrogen or fluoro; R⁵ is hydrogen or fluoro; and R⁶ is hydrogen, fluoro or chloro.
 15. The compound of claim 1, which exhibits a SERT pK_(i)≧7.9 and a NET pK_(i)≧8.
 16. A compound of formula II:

where: (a) R³ and R⁵ are hydrogen and: (i) R⁴ is fluoro, R⁶ is fluoro, and a is 0; (ii) R⁴ is fluoro, R⁶ is fluoro, a is 1, and R¹ is 4-fluoro, 5-fluoro, 5-trifluoromethyl, or 6-fluoro; (iii) R⁴ is fluoro, R⁶ is fluoro, a is 2, and R¹ is 4,5-difluoro, 4,6-difluoro, or 5,6-difluoro; (iv) R⁴ is fluoro, R⁶ is chloro, and a is 0; (v) R⁴ is chloro, R⁶ is fluoro, and a is 0; or (vi) R⁴ is bromo, R⁶ is chloro, and a is 0; or (b) R³ and R⁴ are hydrogen, R⁵ is fluoro, R⁶ is chloro, and: (i) a is 0; (ii) a is 1 and R¹ is 5-fluoro or 6-fluoro; or (iii) a is 2 and R¹ is 4,6-difluoro; or (c) R⁴ and R⁵ are hydrogen, R⁶ is fluoro and; (i) R³ is fluoro and a is 0; (ii) R³ is fluoro, a is 1, and R¹ is 3-fluoro, 5-fluoro, 5-trifluoromethyl, or 6-fluoro; (iii) R³ is fluoro, a is 2, and R¹ is 4,6-difluoro; or (iv) R³ is chloro or methyl, and a is 0; or (d) R³, R⁴, and R⁵ are hydrogen and: (i) R⁶ is H, and a is 0; (ii) R⁶ is H, a is 1, and R¹ is 5-fluoro or 6-fluoro; (iii) R⁶ is fluoro and a is 0; (iv) R⁶ is fluoro, a is 1, and R¹ is 4-fluoro, 5-fluoro, or 6-fluoro; (v) R⁶ is fluoro, a is 2, and R¹ is 4,5-difluoro or 4,6-difluoro; (vi) R⁶ is chloro and a is 0; (vii) R⁶ is chloro, a is 1, and R¹ is 4-fluoro, 6-fluoro, or 5-trifluoromethyl; (viii) R⁶ is chloro, a is 2, and R¹ is 4,5-difluoro; or (ix) R⁶ is bromo and a is 0; or a pharmaceutically acceptable salt thereof.
 17. The compound of claim 16, where R³ and R⁵ are hydrogen, and: (i) R⁴ is fluoro, R⁶ is fluoro, and a is 0; (ii) R⁴ is fluoro, R⁶ is fluoro, a is 1, and R¹ is 4-fluoro, 5-fluoro, 5-trifluoromethyl, or 6-fluoro; (iii) R⁴ is fluoro, R⁶ is fluoro, a is 2, and R¹ is 4,5-difluoro, 4,6-difluoro, or 5,6-difluoro; (iv) R⁴ is fluoro, R⁶ is chloro, and a is 0; (v) R⁴ is chloro, R⁶ is fluoro, and a is 0; or (vi) R⁴ is bromo, R⁶ is chloro, and a is
 0. 18. The compound of claim 17, where R⁴ is fluoro, R⁶ is fluoro, and a is
 0. 19. The compound of claim 16, where R³ and R⁴ are hydrogen, R⁵ is fluoro, R⁶ is chloro, and: (i) a is 0; (ii) a is 1 and R¹ is 5-fluoro or 6-fluoro; or (iii) a is 2 and R¹ is 4,6-difluoro.
 20. The compound of claim 16, where R⁴ and R⁵ are hydrogen, R⁶ is fluoro, and; (i) R³ is fluoro and a is 0; (ii) R³ is fluoro, a is 1, and R¹ is 3-fluoro, 5-fluoro, 5-trifluoromethyl, or 6-fluoro; (iii) R³ is fluoro, a is 2, and R¹ is 4,6-difluoro; or (iv) R³ is chloro or methyl, and a is
 0. 21. The compound of claim 16, where R³, R⁴, and R⁵ are hydrogen, and: (i) R⁶ is H, and a is 0; (ii) R⁶ is H, a is 1, and R¹ is 5-fluoro or 6-fluoro; (iii) R⁶ is fluoro and a is 0; (iv) R⁶ is fluoro, a is 1, and R¹ is 4-fluoro, 5-fluoro, or 6-fluoro; (v) R⁶ is fluoro, a is 2, and R¹ is 4,5-difluoro or 4,6-difluoro; (vi) R⁶ is chloro and a is 0; (vii) R⁶ is chloro, a is 1, and R¹ is 4-fluoro, 6-fluoro, or 5-trifluoromethyl; (viii) R⁶ is chloro, a is 2, and R¹ is 4,5-difluoro; or (ix) R⁶ is bromo and a is
 0. 22. A compound of formula III, useful in the synthesis of the compound of claim 1 or 16:

where P represents an amino-protecting group, or a salt thereof.
 23. The compound of claim 22, where a is 0, R³ and R⁵ are hydrogen, and R⁴ and R⁶ are fluoro.
 24. A method of preparing the compound of claim 1 or 16, the process comprising deprotecting a compound of formula III:

or a salt thereof, where P represents an amino-protecting group, to provide a compound of formula II or I.
 25. The method of claim 24, where a is 0, R³ and R⁵ are hydrogen, and R⁴ and R⁶ are fluoro.
 26. A pharmaceutical composition comprising a compound of claim 1 or 16 and a pharmaceutically acceptable carrier. 